diff --git a/caps/nsScriptSecurityManager.cpp b/caps/nsScriptSecurityManager.cpp
index 2a60221726dd..5e27e73728f6 100644
--- a/caps/nsScriptSecurityManager.cpp
+++ b/caps/nsScriptSecurityManager.cpp
@@ -154,8 +154,8 @@ inline void SetPendingExceptionASCII(JSContext *cx, const char *aMsg)
 
 inline void SetPendingException(JSContext *cx, const char16_t *aMsg)
 {
-    NS_ConvertUTF16toUTF8 msg(aMsg);
-    JS_ReportErrorUTF8(cx, "%s", msg.get());
+    // FIXME: Need to convert to UTF-8 (bug XXX).
+    JS_ReportErrorLatin1(cx, "%hs", aMsg);
 }
 
 // Helper class to get stuff from the ClassInfo and not waste extra time with
diff --git a/dom/plugins/base/nsJSNPRuntime.cpp b/dom/plugins/base/nsJSNPRuntime.cpp
index d9377a70604d..020cffd4e69c 100644
--- a/dom/plugins/base/nsJSNPRuntime.cpp
+++ b/dom/plugins/base/nsJSNPRuntime.cpp
@@ -638,7 +638,7 @@ ThrowJSExceptionASCII(JSContext *cx, const char *message)
 
     PopException();
   } else {
-    ::JS_ReportErrorASCII(cx, "%s", message);
+    ::JS_ReportErrorASCII(cx, message);
   }
 }
 
diff --git a/js/src/asmjs/AsmJS.cpp b/js/src/asmjs/AsmJS.cpp
index e375b49bcb7a..545a95a37842 100644
--- a/js/src/asmjs/AsmJS.cpp
+++ b/js/src/asmjs/AsmJS.cpp
@@ -2250,7 +2250,7 @@ class MOZ_STACK_CLASS ModuleValidator
         return false;
     }
 
-    bool failfOffset(uint32_t offset, const char* fmt, ...) MOZ_FORMAT_PRINTF(3, 4) {
+    bool failfOffset(uint32_t offset, const char* fmt, ...) {
         va_list ap;
         va_start(ap, fmt);
         failfVAOffset(offset, fmt, ap);
@@ -2258,7 +2258,7 @@ class MOZ_STACK_CLASS ModuleValidator
         return false;
     }
 
-    bool failf(ParseNode* pn, const char* fmt, ...) MOZ_FORMAT_PRINTF(3, 4) {
+    bool failf(ParseNode* pn, const char* fmt, ...) {
         va_list ap;
         va_start(ap, fmt);
         failfVAOffset(pn->pn_pos.begin, fmt, ap);
@@ -2944,7 +2944,7 @@ class MOZ_STACK_CLASS FunctionValidator
         return m_.fail(pn, str);
     }
 
-    bool failf(ParseNode* pn, const char* fmt, ...) MOZ_FORMAT_PRINTF(3, 4) {
+    bool failf(ParseNode* pn, const char* fmt, ...) {
         va_list ap;
         va_start(ap, fmt);
         m_.failfVAOffset(pn->pn_pos.begin, fmt, ap);
@@ -4720,8 +4720,7 @@ static bool
 CheckSignatureAgainstExisting(ModuleValidator& m, ParseNode* usepn, const Sig& sig, const Sig& existing)
 {
     if (sig.args().length() != existing.args().length()) {
-        return m.failf(usepn, "incompatible number of arguments (%" PRIuSIZE
-                       " here vs. %" PRIuSIZE " before)",
+        return m.failf(usepn, "incompatible number of arguments (%u here vs. %u before)",
                        sig.args().length(), existing.args().length());
     }
 
diff --git a/js/src/asmjs/WasmBinary.cpp b/js/src/asmjs/WasmBinary.cpp
index f5104f846b3a..4c1946583a6c 100644
--- a/js/src/asmjs/WasmBinary.cpp
+++ b/js/src/asmjs/WasmBinary.cpp
@@ -57,7 +57,7 @@ wasm::DecodePreamble(Decoder& d)
         return d.fail("failed to match magic number");
 
     if (!d.readFixedU32(&u32) || u32 != EncodingVersion)
-        return d.fail("binary version 0x%" PRIx32 " does not match expected version 0x%" PRIx32,
+        return d.fail("binary version 0x%lx does not match expected version 0x%lx",
                       u32, EncodingVersion);
 
     return true;
@@ -151,7 +151,7 @@ wasm::DecodeLimits(Decoder& d, Limits* limits)
     // TODO (bug 1310149): tighten this check (s/3/1) when the AngryBots demo
     // gets updated.
     if (flags & ~uint32_t(0x3))
-        return d.fail("unexpected bits set in flags: %" PRIu32, (flags & ~uint32_t(0x3)));
+        return d.fail("unexpected bits set in flags: %lu", (flags & ~uint32_t(0x3)));
 
     if (!d.readVarU32(&limits->initial))
         return d.fail("expected initial length");
@@ -163,7 +163,7 @@ wasm::DecodeLimits(Decoder& d, Limits* limits)
 
         if (limits->initial > maximum) {
             return d.fail("memory size minimum must not be greater than maximum; "
-                          "maximum length %" PRIu32 " is less than initial length %" PRIu32 ,
+                          "maximum length %lu is less than initial length %lu",
                           maximum, limits->initial);
         }
 
diff --git a/js/src/asmjs/WasmBinary.h b/js/src/asmjs/WasmBinary.h
index 40ad205f73f3..b81121a8b42e 100644
--- a/js/src/asmjs/WasmBinary.h
+++ b/js/src/asmjs/WasmBinary.h
@@ -778,7 +778,7 @@ class Decoder
         error_(error)
     {}
 
-    bool fail(const char* msg, ...) MOZ_FORMAT_PRINTF(2, 3);
+    bool fail(const char* msg, ...);
     bool fail(UniqueChars msg);
     void clearError() {
         if (error_)
diff --git a/js/src/asmjs/WasmBinaryIterator.h b/js/src/asmjs/WasmBinaryIterator.h
index ae244044225c..9a9bf1edfa06 100644
--- a/js/src/asmjs/WasmBinaryIterator.h
+++ b/js/src/asmjs/WasmBinaryIterator.h
@@ -725,7 +725,7 @@ template <typename Policy>
 bool
 ExprIter<Policy>::fail(const char* msg)
 {
-    return d_.fail("%s", msg);
+    return d_.fail(msg);
 }
 
 template <typename Policy>
diff --git a/js/src/asmjs/WasmCode.cpp b/js/src/asmjs/WasmCode.cpp
index 619dba2b921e..3b0b37c8c1af 100644
--- a/js/src/asmjs/WasmCode.cpp
+++ b/js/src/asmjs/WasmCode.cpp
@@ -796,10 +796,8 @@ Code::ensureProfilingState(JSContext* cx, bool newProfilingEnabled)
             if (!name.append('\0'))
                 return false;
 
-            TwoByteChars chars(name.begin(), name.length());
-            UniqueChars utf8Name(JS::CharsToNewUTF8CharsZ(nullptr, chars).c_str());
-            UniqueChars label(JS_smprintf("%s (%s:%u)",
-                                          utf8Name.get(),
+            UniqueChars label(JS_smprintf("%hs (%s:%u)",
+                                          name.begin(),
                                           metadata_->filename.get(),
                                           codeRange.funcLineOrBytecode()));
             if (!label) {
diff --git a/js/src/asmjs/WasmTextToBinary.cpp b/js/src/asmjs/WasmTextToBinary.cpp
index 6ac574544680..822654924e8f 100644
--- a/js/src/asmjs/WasmTextToBinary.cpp
+++ b/js/src/asmjs/WasmTextToBinary.cpp
@@ -1488,7 +1488,7 @@ struct WasmParseContext
     {}
 
     bool fail(const char* message) {
-        error->reset(js_strdup(message));
+        error->reset(JS_smprintf(message));
         return false;
     }
     ~WasmParseContext() {
@@ -3336,9 +3336,12 @@ class Resolver
         return false;
     }
     bool failResolveLabel(const char* kind, AstName name) {
-        TwoByteChars chars(name.begin(), name.length());
-        UniqueChars utf8Chars(CharsToNewUTF8CharsZ(nullptr, chars).c_str());
-        error_->reset(JS_smprintf("%s label '%s' not found", kind, utf8Chars.get()));
+        Vector<char16_t, 0, SystemAllocPolicy> nameWithNull;
+        if (!nameWithNull.append(name.begin(), name.length()))
+            return false;
+        if (!nameWithNull.append(0))
+            return false;
+        error_->reset(JS_smprintf("%s label '%hs' not found", kind, nameWithNull.begin()));
         return false;
     }
 
diff --git a/js/src/devtools/gctrace/gcstats.cpp b/js/src/devtools/gctrace/gcstats.cpp
index 865e65839dea..9b7d22247aef 100644
--- a/js/src/devtools/gctrace/gcstats.cpp
+++ b/js/src/devtools/gctrace/gcstats.cpp
@@ -165,7 +165,6 @@ Array<Array<uint64_t, MaxLifetimeBins>, MaxClasses> finalizedHeapObjectCountByCl
 std::vector<Array<Array<uint64_t, MaxLifetimeBins>, HeapKinds> > objectCountByTypeHeapAndLifetime;
 
 static void
-MOZ_FORMAT_PRINTF(1, 2)
 die(const char* format, ...)
 {
     va_list va;
diff --git a/js/src/irregexp/RegExpEngine.cpp b/js/src/irregexp/RegExpEngine.cpp
index bc556b4a1ef2..623525d2215a 100644
--- a/js/src/irregexp/RegExpEngine.cpp
+++ b/js/src/irregexp/RegExpEngine.cpp
@@ -1872,7 +1872,7 @@ irregexp::CompilePattern(JSContext* cx, RegExpShared* shared, RegExpCompileData*
     Analysis analysis(cx, ignore_case, is_ascii, unicode);
     analysis.EnsureAnalyzed(node);
     if (analysis.has_failed()) {
-        JS_ReportErrorASCII(cx, "%s", analysis.errorMessage());
+        JS_ReportErrorASCII(cx, analysis.errorMessage());
         return RegExpCode();
     }
 
diff --git a/js/src/jit/BacktrackingAllocator.cpp b/js/src/jit/BacktrackingAllocator.cpp
index bb5dfac3624f..8d2bca22bf67 100644
--- a/js/src/jit/BacktrackingAllocator.cpp
+++ b/js/src/jit/BacktrackingAllocator.cpp
@@ -1245,7 +1245,7 @@ bool
 BacktrackingAllocator::processBundle(MIRGenerator* mir, LiveBundle* bundle)
 {
     if (JitSpewEnabled(JitSpew_RegAlloc)) {
-        JitSpew(JitSpew_RegAlloc, "Allocating %s [priority %" PRIuSIZE "] [weight %" PRIuSIZE "]",
+        JitSpew(JitSpew_RegAlloc, "Allocating %s [priority %lu] [weight %lu]",
                 bundle->toString().get(), computePriority(bundle), computeSpillWeight(bundle));
     }
 
@@ -1437,13 +1437,13 @@ BacktrackingAllocator::tryAllocateRegister(PhysicalRegister& r, LiveBundle* bund
         if (JitSpewEnabled(JitSpew_RegAlloc)) {
             if (aliasedConflicting.length() == 1) {
                 LiveBundle* existing = aliasedConflicting[0];
-                JitSpew(JitSpew_RegAlloc, "  %s collides with %s [weight %" PRIuSIZE "]",
+                JitSpew(JitSpew_RegAlloc, "  %s collides with %s [weight %lu]",
                         r.reg.name(), existing->toString().get(), computeSpillWeight(existing));
             } else {
                 JitSpew(JitSpew_RegAlloc, "  %s collides with the following", r.reg.name());
                 for (size_t i = 0; i < aliasedConflicting.length(); i++) {
                     LiveBundle* existing = aliasedConflicting[i];
-                    JitSpew(JitSpew_RegAlloc, "      %s [weight %" PRIuSIZE "]",
+                    JitSpew(JitSpew_RegAlloc, "      %s [weight %lu]",
                             existing->toString().get(), computeSpillWeight(existing));
                 }
             }
@@ -1482,7 +1482,7 @@ bool
 BacktrackingAllocator::evictBundle(LiveBundle* bundle)
 {
     if (JitSpewEnabled(JitSpew_RegAlloc)) {
-        JitSpew(JitSpew_RegAlloc, "  Evicting %s [priority %" PRIuSIZE "] [weight %" PRIuSIZE "]",
+        JitSpew(JitSpew_RegAlloc, "  Evicting %s [priority %lu] [weight %lu]",
                 bundle->toString().get(), computePriority(bundle), computeSpillWeight(bundle));
     }
 
@@ -2296,8 +2296,7 @@ LiveBundle::toString() const
 {
     AutoEnterOOMUnsafeRegion oomUnsafe;
 
-    // Suppress -Wformat warning.
-    char *buf = JS_smprintf("%s", "");
+    char *buf = JS_smprintf("");
 
     for (LiveRange::BundleLinkIterator iter = rangesBegin(); buf && iter; iter++) {
         buf = JS_sprintf_append(buf, "%s %s",
diff --git a/js/src/jit/BaselineBailouts.cpp b/js/src/jit/BaselineBailouts.cpp
index 0b081c265483..4c990b61de55 100644
--- a/js/src/jit/BaselineBailouts.cpp
+++ b/js/src/jit/BaselineBailouts.cpp
@@ -230,11 +230,11 @@ struct BaselineStackBuilder
         if (info) {
             if (sizeof(size_t) == 4) {
                 JitSpew(JitSpew_BaselineBailouts,
-                        "      WRITE_WRD %p/%p %-15s %08" PRIxSIZE,
+                        "      WRITE_WRD %p/%p %-15s %08x",
                         header_->copyStackBottom, virtualPointerAtStackOffset(0), info, w);
             } else {
                 JitSpew(JitSpew_BaselineBailouts,
-                        "      WRITE_WRD %p/%p %-15s %016" PRIxSIZE,
+                        "      WRITE_WRD %p/%p %-15s %016llx",
                         header_->copyStackBottom, virtualPointerAtStackOffset(0), info, w);
             }
         }
@@ -246,7 +246,7 @@ struct BaselineStackBuilder
             return false;
         if (info) {
             JitSpew(JitSpew_BaselineBailouts,
-                    "      WRITE_VAL %p/%p %-15s %016" PRIx64,
+                    "      WRITE_VAL %p/%p %-15s %016llx",
                     header_->copyStackBottom, virtualPointerAtStackOffset(0), info,
                     *((uint64_t*) &val));
         }
@@ -637,7 +637,7 @@ InitFromBailout(JSContext* cx, HandleScript caller, jsbytecode* callerPC,
     // |  ReturnAddr   | <-- return into main jitcode after IC
     // +===============+
 
-    JitSpew(JitSpew_BaselineBailouts, "      Unpacking %s:%" PRIuSIZE, script->filename(), script->lineno());
+    JitSpew(JitSpew_BaselineBailouts, "      Unpacking %s:%d", script->filename(), script->lineno());
     JitSpew(JitSpew_BaselineBailouts, "      [BASELINE-JS FRAME]");
 
     // Calculate and write the previous frame pointer value.
@@ -749,7 +749,7 @@ InitFromBailout(JSContext* cx, HandleScript caller, jsbytecode* callerPC,
     }
     JitSpew(JitSpew_BaselineBailouts, "      EnvChain=%p", envChain);
     blFrame->setEnvironmentChain(envChain);
-    JitSpew(JitSpew_BaselineBailouts, "      ReturnValue=%016" PRIx64, *((uint64_t*) &returnValue));
+    JitSpew(JitSpew_BaselineBailouts, "      ReturnValue=%016llx", *((uint64_t*) &returnValue));
     blFrame->setReturnValue(returnValue);
 
     // Do not need to initialize scratchValue field in BaselineFrame.
@@ -764,13 +764,13 @@ InitFromBailout(JSContext* cx, HandleScript caller, jsbytecode* callerPC,
         // in the calling frame.
         Value thisv = iter.read();
         JitSpew(JitSpew_BaselineBailouts, "      Is function!");
-        JitSpew(JitSpew_BaselineBailouts, "      thisv=%016" PRIx64, *((uint64_t*) &thisv));
+        JitSpew(JitSpew_BaselineBailouts, "      thisv=%016llx", *((uint64_t*) &thisv));
 
         size_t thisvOffset = builder.framePushed() + JitFrameLayout::offsetOfThis();
         builder.valuePointerAtStackOffset(thisvOffset).set(thisv);
 
         MOZ_ASSERT(iter.numAllocations() >= CountArgSlots(script, fun));
-        JitSpew(JitSpew_BaselineBailouts, "      frame slots %u, nargs %" PRIuSIZE ", nfixed %" PRIuSIZE,
+        JitSpew(JitSpew_BaselineBailouts, "      frame slots %u, nargs %u, nfixed %u",
                 iter.numAllocations(), fun->nargs(), script->nfixed());
 
         if (!callerPC) {
@@ -786,7 +786,7 @@ InitFromBailout(JSContext* cx, HandleScript caller, jsbytecode* callerPC,
 
         for (uint32_t i = 0; i < fun->nargs(); i++) {
             Value arg = iter.read();
-            JitSpew(JitSpew_BaselineBailouts, "      arg %d = %016" PRIx64,
+            JitSpew(JitSpew_BaselineBailouts, "      arg %d = %016llx",
                         (int) i, *((uint64_t*) &arg));
             if (callerPC) {
                 size_t argOffset = builder.framePushed() + JitFrameLayout::offsetOfActualArg(i);
@@ -1314,7 +1314,7 @@ InitFromBailout(JSContext* cx, HandleScript caller, jsbytecode* callerPC,
         return false;
 
     // Push callee token (must be a JS Function)
-    JitSpew(JitSpew_BaselineBailouts, "      Callee = %016" PRIx64, callee.asRawBits());
+    JitSpew(JitSpew_BaselineBailouts, "      Callee = %016llx", callee.asRawBits());
 
     JSFunction* calleeFun = &callee.toObject().as<JSFunction>();
     if (!builder.writePtr(CalleeToToken(calleeFun, JSOp(*pc) == JSOP_NEW), "CalleeToken"))
@@ -1494,7 +1494,7 @@ jit::BailoutIonToBaseline(JSContext* cx, JitActivation* activation, JitFrameIter
     //      |    |||||      |
     //      +---------------+
 
-    JitSpew(JitSpew_BaselineBailouts, "Bailing to baseline %s:%" PRIuSIZE " (IonScript=%p) (FrameType=%d)",
+    JitSpew(JitSpew_BaselineBailouts, "Bailing to baseline %s:%u (IonScript=%p) (FrameType=%d)",
             iter.script()->filename(), iter.script()->lineno(), (void*) iter.ionScript(),
             (int) prevFrameType);
 
@@ -1514,7 +1514,7 @@ jit::BailoutIonToBaseline(JSContext* cx, JitActivation* activation, JitFrameIter
         propagatingExceptionForDebugMode = false;
     }
 
-    JitSpew(JitSpew_BaselineBailouts, "  Reading from snapshot offset %u size %" PRIuSIZE,
+    JitSpew(JitSpew_BaselineBailouts, "  Reading from snapshot offset %u size %u",
             iter.snapshotOffset(), iter.ionScript()->snapshotsListSize());
 
     if (!excInfo)
@@ -1540,7 +1540,7 @@ jit::BailoutIonToBaseline(JSContext* cx, JitActivation* activation, JitFrameIter
     RootedFunction callee(cx, iter.maybeCallee());
     RootedScript scr(cx, iter.script());
     if (callee) {
-        JitSpew(JitSpew_BaselineBailouts, "  Callee function (%s:%" PRIuSIZE ")",
+        JitSpew(JitSpew_BaselineBailouts, "  Callee function (%s:%u)",
                 scr->filename(), scr->lineno());
     } else {
         JitSpew(JitSpew_BaselineBailouts, "  No callee!");
@@ -1575,7 +1575,7 @@ jit::BailoutIonToBaseline(JSContext* cx, JitActivation* activation, JitFrameIter
             TraceLogStartEvent(logger, TraceLogger_Baseline);
         }
 
-        JitSpew(JitSpew_BaselineBailouts, "    FrameNo %" PRIuSIZE, frameNo);
+        JitSpew(JitSpew_BaselineBailouts, "    FrameNo %d", frameNo);
 
         // If we are bailing out to a catch or finally block in this frame,
         // pass excInfo to InitFromBailout and don't unpack any other frames.
@@ -1671,7 +1671,7 @@ InvalidateAfterBailout(JSContext* cx, HandleScript outerScript, const char* reas
 static void
 HandleBoundsCheckFailure(JSContext* cx, HandleScript outerScript, HandleScript innerScript)
 {
-    JitSpew(JitSpew_IonBailouts, "Bounds check failure %s:%" PRIuSIZE ", inlined into %s:%" PRIuSIZE,
+    JitSpew(JitSpew_IonBailouts, "Bounds check failure %s:%d, inlined into %s:%d",
             innerScript->filename(), innerScript->lineno(),
             outerScript->filename(), outerScript->lineno());
 
@@ -1686,7 +1686,7 @@ HandleBoundsCheckFailure(JSContext* cx, HandleScript outerScript, HandleScript i
 static void
 HandleShapeGuardFailure(JSContext* cx, HandleScript outerScript, HandleScript innerScript)
 {
-    JitSpew(JitSpew_IonBailouts, "Shape guard failure %s:%" PRIuSIZE ", inlined into %s:%" PRIuSIZE,
+    JitSpew(JitSpew_IonBailouts, "Shape guard failure %s:%d, inlined into %s:%d",
             innerScript->filename(), innerScript->lineno(),
             outerScript->filename(), outerScript->lineno());
 
@@ -1701,7 +1701,7 @@ HandleShapeGuardFailure(JSContext* cx, HandleScript outerScript, HandleScript in
 static void
 HandleBaselineInfoBailout(JSContext* cx, HandleScript outerScript, HandleScript innerScript)
 {
-    JitSpew(JitSpew_IonBailouts, "Baseline info failure %s:%" PRIuSIZE ", inlined into %s:%" PRIuSIZE,
+    JitSpew(JitSpew_IonBailouts, "Baseline info failure %s:%d, inlined into %s:%d",
             innerScript->filename(), innerScript->lineno(),
             outerScript->filename(), outerScript->lineno());
 
@@ -1711,7 +1711,7 @@ HandleBaselineInfoBailout(JSContext* cx, HandleScript outerScript, HandleScript
 static void
 HandleLexicalCheckFailure(JSContext* cx, HandleScript outerScript, HandleScript innerScript)
 {
-    JitSpew(JitSpew_IonBailouts, "Lexical check failure %s:%" PRIuSIZE ", inlined into %s:%" PRIuSIZE,
+    JitSpew(JitSpew_IonBailouts, "Lexical check failure %s:%d, inlined into %s:%d",
             innerScript->filename(), innerScript->lineno(),
             outerScript->filename(), outerScript->lineno());
 
@@ -1754,7 +1754,7 @@ CopyFromRematerializedFrame(JSContext* cx, JitActivation* act, uint8_t* fp, size
         frame->setHasCachedSavedFrame();
 
     JitSpew(JitSpew_BaselineBailouts,
-            "  Copied from rematerialized frame at (%p,%" PRIuSIZE ")",
+            "  Copied from rematerialized frame at (%p,%u)",
             fp, inlineDepth);
 
     // Propagate the debuggee frame flag. For the case where the Debugger did
@@ -1891,7 +1891,7 @@ jit::FinishBailoutToBaseline(BaselineBailoutInfo* bailoutInfo)
     }
 
     JitSpew(JitSpew_BaselineBailouts,
-            "  Restored outerScript=(%s:%" PRIuSIZE ",%u) innerScript=(%s:%" PRIuSIZE ",%u) (bailoutKind=%u)",
+            "  Restored outerScript=(%s:%u,%u) innerScript=(%s:%u,%u) (bailoutKind=%u)",
             outerScript->filename(), outerScript->lineno(), outerScript->getWarmUpCount(),
             innerScript->filename(), innerScript->lineno(), innerScript->getWarmUpCount(),
             (unsigned) bailoutKind);
diff --git a/js/src/jit/BaselineCompiler.cpp b/js/src/jit/BaselineCompiler.cpp
index 846a6cd3c816..5c9174655a9a 100644
--- a/js/src/jit/BaselineCompiler.cpp
+++ b/js/src/jit/BaselineCompiler.cpp
@@ -7,7 +7,6 @@
 #include "jit/BaselineCompiler.h"
 
 #include "mozilla/Casting.h"
-#include "mozilla/SizePrintfMacros.h"
 
 #include "jit/BaselineIC.h"
 #include "jit/BaselineJIT.h"
@@ -83,10 +82,10 @@ BaselineCompiler::addPCMappingEntry(bool addIndexEntry)
 MethodStatus
 BaselineCompiler::compile()
 {
-    JitSpew(JitSpew_BaselineScripts, "Baseline compiling script %s:%" PRIuSIZE " (%p)",
+    JitSpew(JitSpew_BaselineScripts, "Baseline compiling script %s:%d (%p)",
             script->filename(), script->lineno(), script);
 
-    JitSpew(JitSpew_Codegen, "# Emitting baseline code for script %s:%" PRIuSIZE,
+    JitSpew(JitSpew_Codegen, "# Emitting baseline code for script %s:%d",
             script->filename(), script->lineno());
 
     TraceLoggerThread* logger = TraceLoggerForMainThread(cx->runtime());
@@ -218,7 +217,7 @@ BaselineCompiler::compile()
     baselineScript->setMethod(code);
     baselineScript->setTemplateEnvironment(templateEnv);
 
-    JitSpew(JitSpew_BaselineScripts, "Created BaselineScript %p (raw %p) for %s:%" PRIuSIZE,
+    JitSpew(JitSpew_BaselineScripts, "Created BaselineScript %p (raw %p) for %s:%d",
             (void*) baselineScript.get(), (void*) code->raw(),
             script->filename(), script->lineno());
 
@@ -280,7 +279,7 @@ BaselineCompiler::compile()
     // Always register a native => bytecode mapping entry, since profiler can be
     // turned on with baseline jitcode on stack, and baseline jitcode cannot be invalidated.
     {
-        JitSpew(JitSpew_Profiling, "Added JitcodeGlobalEntry for baseline script %s:%" PRIuSIZE " (%p)",
+        JitSpew(JitSpew_Profiling, "Added JitcodeGlobalEntry for baseline script %s:%d (%p)",
                     script->filename(), script->lineno(), baselineScript.get());
 
         // Generate profiling string.
diff --git a/js/src/jit/BaselineDebugModeOSR.cpp b/js/src/jit/BaselineDebugModeOSR.cpp
index 8b937ee24591..889f44dc9b70 100644
--- a/js/src/jit/BaselineDebugModeOSR.cpp
+++ b/js/src/jit/BaselineDebugModeOSR.cpp
@@ -7,7 +7,6 @@
 #include "jit/BaselineDebugModeOSR.h"
 
 #include "mozilla/DebugOnly.h"
-#include "mozilla/SizePrintfMacros.h"
 
 #include "jit/BaselineIC.h"
 #include "jit/JitcodeMap.h"
@@ -323,7 +322,7 @@ SpewPatchBaselineFrame(uint8_t* oldReturnAddress, uint8_t* newReturnAddress,
                        JSScript* script, ICEntry::Kind frameKind, jsbytecode* pc)
 {
     JitSpew(JitSpew_BaselineDebugModeOSR,
-            "Patch return %p -> %p on BaselineJS frame (%s:%" PRIuSIZE ") from %s at %s",
+            "Patch return %p -> %p on BaselineJS frame (%s:%d) from %s at %s",
             oldReturnAddress, newReturnAddress, script->filename(), script->lineno(),
             ICEntryKindToString(frameKind), CodeName[(JSOp)*pc]);
 }
@@ -333,7 +332,7 @@ SpewPatchBaselineFrameFromExceptionHandler(uint8_t* oldReturnAddress, uint8_t* n
                                            JSScript* script, jsbytecode* pc)
 {
     JitSpew(JitSpew_BaselineDebugModeOSR,
-            "Patch return %p -> %p on BaselineJS frame (%s:%" PRIuSIZE ") from exception handler at %s",
+            "Patch return %p -> %p on BaselineJS frame (%s:%d) from exception handler at %s",
             oldReturnAddress, newReturnAddress, script->filename(), script->lineno(),
             CodeName[(JSOp)*pc]);
 }
@@ -668,7 +667,7 @@ RecompileBaselineScriptForDebugMode(JSContext* cx, JSScript* script,
     if (oldBaselineScript->hasDebugInstrumentation() == observing)
         return true;
 
-    JitSpew(JitSpew_BaselineDebugModeOSR, "Recompiling (%s:%" PRIuSIZE ") for %s",
+    JitSpew(JitSpew_BaselineDebugModeOSR, "Recompiling (%s:%d) for %s",
             script->filename(), script->lineno(), observing ? "DEBUGGING" : "NORMAL EXECUTION");
 
     script->setBaselineScript(cx->runtime(), nullptr);
diff --git a/js/src/jit/BaselineIC.cpp b/js/src/jit/BaselineIC.cpp
index 4f43c18989d0..5835283268d4 100644
--- a/js/src/jit/BaselineIC.cpp
+++ b/js/src/jit/BaselineIC.cpp
@@ -2586,7 +2586,7 @@ DoSetElemFallback(JSContext* cx, BaselineFrame* frame, ICSetElem_Fallback* stub_
             {
                 JitSpew(JitSpew_BaselineIC,
                         "  Generating SetElem_DenseOrUnboxedArrayAdd stub "
-                        "(shape=%p, group=%p, protoDepth=%" PRIuSIZE ")",
+                        "(shape=%p, group=%p, protoDepth=%u)",
                         shape.get(), group.get(), protoDepth);
                 ICSetElemDenseOrUnboxedArrayAddCompiler compiler(cx, obj, protoDepth);
                 ICUpdatedStub* newStub = compiler.getStub(compiler.getStubSpace(outerScript));
diff --git a/js/src/jit/CodeGenerator.cpp b/js/src/jit/CodeGenerator.cpp
index 72018eacd719..680748482a3c 100644
--- a/js/src/jit/CodeGenerator.cpp
+++ b/js/src/jit/CodeGenerator.cpp
@@ -9244,7 +9244,7 @@ CodeGenerator::generateWasm(wasm::SigIdDesc sigId, wasm::TrapOffset trapOffset,
 bool
 CodeGenerator::generate()
 {
-    JitSpew(JitSpew_Codegen, "# Emitting code for script %s:%" PRIuSIZE,
+    JitSpew(JitSpew_Codegen, "# Emitting code for script %s:%d",
             gen->info().script()->filename(),
             gen->info().script()->lineno());
 
diff --git a/js/src/jit/FlowAliasAnalysis.cpp b/js/src/jit/FlowAliasAnalysis.cpp
index 2b88e36785af..e237163bb7f8 100644
--- a/js/src/jit/FlowAliasAnalysis.cpp
+++ b/js/src/jit/FlowAliasAnalysis.cpp
@@ -402,7 +402,7 @@ DumpImprovement(MDefinition *load, MDefinitionVector& input, MDefinitionVector&
     if (JitSpewEnabled(JitSpew_Alias)) {
         Fprinter &print = JitSpewPrinter();
         JitSpewHeader(JitSpew_Alias);
-        print.printf("   Improve dependency from %d", load->id());
+        print.printf("   Improve dependency from ", load->id());
         DumpStoreList(input);
         print.printf(" to ");
         DumpStoreList(output);
diff --git a/js/src/jit/Ion.cpp b/js/src/jit/Ion.cpp
index 13c20fc41edd..6e164d058f6f 100644
--- a/js/src/jit/Ion.cpp
+++ b/js/src/jit/Ion.cpp
@@ -6,7 +6,6 @@
 
 #include "jit/Ion.h"
 
-#include "mozilla/IntegerPrintfMacros.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/SizePrintfMacros.h"
 #include "mozilla/ThreadLocal.h"
@@ -2137,7 +2136,7 @@ TrackIonAbort(JSContext* cx, JSScript* script, jsbytecode* pc, const char* messa
 static void
 TrackAndSpewIonAbort(JSContext* cx, JSScript* script, const char* message)
 {
-    JitSpew(JitSpew_IonAbort, "%s", message);
+    JitSpew(JitSpew_IonAbort, message);
     TrackIonAbort(cx, script, script->code(), message);
 }
 
@@ -2396,7 +2395,7 @@ CheckScriptSize(JSContext* cx, JSScript* script)
         numLocalsAndArgs > MAX_MAIN_THREAD_LOCALS_AND_ARGS)
     {
         if (!OffThreadCompilationAvailable(cx)) {
-            JitSpew(JitSpew_IonAbort, "Script too large (%" PRIuSIZE " bytes) (%u locals/args)",
+            JitSpew(JitSpew_IonAbort, "Script too large (%u bytes) (%u locals/args)",
                     script->length(), numLocalsAndArgs);
             TrackIonAbort(cx, script, script->code(), "too large");
             return Method_CantCompile;
@@ -3015,7 +3014,7 @@ InvalidateActivation(FreeOp* fop, const JitActivationIterator& activations, bool
 #ifdef JS_JITSPEW
         switch (it.type()) {
           case JitFrame_Exit:
-            JitSpew(JitSpew_IonInvalidate, "#%" PRIuSIZE " exit frame @ %p", frameno, it.fp());
+            JitSpew(JitSpew_IonInvalidate, "#%d exit frame @ %p", frameno, it.fp());
             break;
           case JitFrame_BaselineJS:
           case JitFrame_IonJS:
@@ -3030,26 +3029,26 @@ InvalidateActivation(FreeOp* fop, const JitActivationIterator& activations, bool
             else if (it.isBailoutJS())
                 type = "Bailing";
             JitSpew(JitSpew_IonInvalidate,
-                    "#%" PRIuSIZE " %s JS frame @ %p, %s:%" PRIuSIZE " (fun: %p, script: %p, pc %p)",
+                    "#%d %s JS frame @ %p, %s:%" PRIuSIZE " (fun: %p, script: %p, pc %p)",
                     frameno, type, it.fp(), it.script()->maybeForwardedFilename(),
                     it.script()->lineno(), it.maybeCallee(), (JSScript*)it.script(),
                     it.returnAddressToFp());
             break;
           }
           case JitFrame_IonStub:
-            JitSpew(JitSpew_IonInvalidate, "#%" PRIuSIZE " ion stub frame @ %p", frameno, it.fp());
+            JitSpew(JitSpew_IonInvalidate, "#%d ion stub frame @ %p", frameno, it.fp());
             break;
           case JitFrame_BaselineStub:
-            JitSpew(JitSpew_IonInvalidate, "#%" PRIuSIZE " baseline stub frame @ %p", frameno, it.fp());
+            JitSpew(JitSpew_IonInvalidate, "#%d baseline stub frame @ %p", frameno, it.fp());
             break;
           case JitFrame_Rectifier:
-            JitSpew(JitSpew_IonInvalidate, "#%" PRIuSIZE " rectifier frame @ %p", frameno, it.fp());
+            JitSpew(JitSpew_IonInvalidate, "#%d rectifier frame @ %p", frameno, it.fp());
             break;
           case JitFrame_IonAccessorIC:
-            JitSpew(JitSpew_IonInvalidate, "#%" PRIuSIZE " ion IC getter/setter frame @ %p", frameno, it.fp());
+            JitSpew(JitSpew_IonInvalidate, "#%d ion IC getter/setter frame @ %p", frameno, it.fp());
             break;
           case JitFrame_Entry:
-            JitSpew(JitSpew_IonInvalidate, "#%" PRIuSIZE " entry frame @ %p", frameno, it.fp());
+            JitSpew(JitSpew_IonInvalidate, "#%d entry frame @ %p", frameno, it.fp());
             break;
         }
 #endif // JS_JITSPEW
@@ -3144,7 +3143,7 @@ InvalidateActivation(FreeOp* fop, const JitActivationIterator& activations, bool
         CodeLocationLabel osiPatchPoint = SafepointReader::InvalidationPatchPoint(ionScript, si);
         CodeLocationLabel invalidateEpilogue(ionCode, CodeOffset(ionScript->invalidateEpilogueOffset()));
 
-        JitSpew(JitSpew_IonInvalidate, "   ! Invalidate ionScript %p (inv count %" PRIuSIZE ") -> patching osipoint %p",
+        JitSpew(JitSpew_IonInvalidate, "   ! Invalidate ionScript %p (inv count %u) -> patching osipoint %p",
                 ionScript, ionScript->invalidationCount(), (void*) osiPatchPoint.raw());
         Assembler::PatchWrite_NearCall(osiPatchPoint, invalidateEpilogue);
     }
@@ -3361,7 +3360,7 @@ AutoFlushICache::setRange(uintptr_t start, size_t len)
     AutoFlushICache* afc = TlsPerThreadData.get()->PerThreadData::autoFlushICache();
     MOZ_ASSERT(afc);
     MOZ_ASSERT(!afc->start_);
-    JitSpewCont(JitSpew_CacheFlush, "(%" PRIxPTR " %" PRIxSIZE "):", start, len);
+    JitSpewCont(JitSpew_CacheFlush, "(%x %x):", start, len);
 
     uintptr_t stop = start + len;
     afc->start_ = start;
diff --git a/js/src/jit/IonAnalysis.cpp b/js/src/jit/IonAnalysis.cpp
index 294331b10865..e683b9fb695d 100644
--- a/js/src/jit/IonAnalysis.cpp
+++ b/js/src/jit/IonAnalysis.cpp
@@ -6,8 +6,6 @@
 
 #include "jit/IonAnalysis.h"
 
-#include "mozilla/SizePrintfMacros.h"
-
 #include "jit/AliasAnalysis.h"
 #include "jit/BaselineInspector.h"
 #include "jit/BaselineJIT.h"
@@ -447,10 +445,9 @@ jit::PruneUnusedBranches(MIRGenerator* mir, MIRGraph& graph)
                 shouldBailout = false;
 
             JitSpew(JitSpew_Prune, "info: block %d,"
-                    " predCount: %" PRIuSIZE ", domInst: %" PRIuSIZE
-                    ", span: %" PRIuSIZE ", effectful: %" PRIuSIZE ", "
-                    " isLoopExit: %s, numSuccessorsOfPred: %" PRIuSIZE "."
-                    " (score: %" PRIuSIZE ", shouldBailout: %s)",
+                    " predCount: %lu, domInst: %lu, span: %lu, effectful: %lu, "
+                    " isLoopExit: %s, numSuccessorsOfPred: %lu."
+                    " (score: %lu, shouldBailout: %s)",
                     block->id(), predCount, numDominatedInst, branchSpan, numEffectfulInst,
                     isLoopExit ? "true" : "false", numSuccessorsOfPreds,
                     score, shouldBailout ? "true" : "false");
diff --git a/js/src/jit/IonBuilder.h b/js/src/jit/IonBuilder.h
index 868d9e8e497f..42797a84c8bd 100644
--- a/js/src/jit/IonBuilder.h
+++ b/js/src/jit/IonBuilder.h
@@ -229,7 +229,7 @@ class IonBuilder
     MOZ_MUST_USE bool inspectOpcode(JSOp op);
     uint32_t readIndex(jsbytecode* pc);
     JSAtom* readAtom(jsbytecode* pc);
-    bool abort(const char* message, ...) MOZ_FORMAT_PRINTF(2, 3);
+    bool abort(const char* message, ...);
     void trackActionableAbort(const char* message);
     void spew(const char* message);
 
diff --git a/js/src/jit/JSONSpewer.cpp b/js/src/jit/JSONSpewer.cpp
index 330b419f5774..d6105f498bab 100644
--- a/js/src/jit/JSONSpewer.cpp
+++ b/js/src/jit/JSONSpewer.cpp
@@ -8,8 +8,6 @@
 
 #include "jit/JSONSpewer.h"
 
-#include "mozilla/SizePrintfMacros.h"
-
 #include <stdarg.h>
 
 #include "jit/BacktrackingAllocator.h"
@@ -148,7 +146,7 @@ JSONSpewer::beginFunction(JSScript* script)
 {
     beginObject();
     if (script)
-        stringProperty("name", "%s:%" PRIuSIZE, script->filename(), script->lineno());
+        stringProperty("name", "%s:%d", script->filename(), script->lineno());
     else
         stringProperty("name", "asm.js compilation");
     beginListProperty("passes");
@@ -158,7 +156,7 @@ void
 JSONSpewer::beginPass(const char* pass)
 {
     beginObject();
-    stringProperty("name", "%s", pass);
+    stringProperty("name", pass);
 }
 
 void
diff --git a/js/src/jit/JSONSpewer.h b/js/src/jit/JSONSpewer.h
index 02f449c7ab04..f4172c6b46ed 100644
--- a/js/src/jit/JSONSpewer.h
+++ b/js/src/jit/JSONSpewer.h
@@ -36,8 +36,8 @@ class JSONSpewer
     void beginObject();
     void beginObjectProperty(const char* name);
     void beginListProperty(const char* name);
-    void stringValue(const char* format, ...) MOZ_FORMAT_PRINTF(2, 3);
-    void stringProperty(const char* name, const char* format, ...) MOZ_FORMAT_PRINTF(3, 4);
+    void stringValue(const char* format, ...);
+    void stringProperty(const char* name, const char* format, ...);
     void beginStringProperty(const char* name);
     void endStringProperty();
     void integerValue(int value);
diff --git a/js/src/jit/JitSpewer.h b/js/src/jit/JitSpewer.h
index a44eec4662f9..024e7d5a1ff8 100644
--- a/js/src/jit/JitSpewer.h
+++ b/js/src/jit/JitSpewer.h
@@ -172,9 +172,9 @@ class JitSpewIndent
     ~JitSpewIndent();
 };
 
-void JitSpew(JitSpewChannel channel, const char* fmt, ...) MOZ_FORMAT_PRINTF(2, 3);
-void JitSpewStart(JitSpewChannel channel, const char* fmt, ...) MOZ_FORMAT_PRINTF(2, 3);
-void JitSpewCont(JitSpewChannel channel, const char* fmt, ...) MOZ_FORMAT_PRINTF(2, 3);
+void JitSpew(JitSpewChannel channel, const char* fmt, ...);
+void JitSpewStart(JitSpewChannel channel, const char* fmt, ...);
+void JitSpewCont(JitSpewChannel channel, const char* fmt, ...);
 void JitSpewFin(JitSpewChannel channel);
 void JitSpewHeader(JitSpewChannel channel);
 bool JitSpewEnabled(JitSpewChannel channel);
diff --git a/js/src/jit/MIRGenerator.h b/js/src/jit/MIRGenerator.h
index 342ff2945431..2aedc1a924a6 100644
--- a/js/src/jit/MIRGenerator.h
+++ b/js/src/jit/MIRGenerator.h
@@ -72,7 +72,7 @@ class MIRGenerator
 
     // Set an error state and prints a message. Returns false so errors can be
     // propagated up.
-    bool abort(const char* message, ...) MOZ_FORMAT_PRINTF(2, 3); // always returns false
+    bool abort(const char* message, ...);           // always returns false
     bool abortFmt(const char* message, va_list ap); // always returns false
 
     bool errored() const {
diff --git a/js/src/jit/OptimizationTracking.cpp b/js/src/jit/OptimizationTracking.cpp
index 8ef16e33938a..029b3c082be1 100644
--- a/js/src/jit/OptimizationTracking.cpp
+++ b/js/src/jit/OptimizationTracking.cpp
@@ -326,7 +326,7 @@ UniqueTrackedOptimizations::sortByFrequency(JSContext* cx)
         MOZ_ASSERT(p);
         p->value().index = sorted_.length();
 
-        JitSpew(JitSpew_OptimizationTracking, "   Entry %" PRIuSIZE " has frequency %" PRIu32,
+        JitSpew(JitSpew_OptimizationTracking, "   Entry %u has frequency %u",
                 sorted_.length(), p->value().frequency);
 
         if (!sorted_.append(entries[i]))
@@ -765,14 +765,14 @@ IonTrackedOptimizationsRegion::WriteRun(CompactBufferWriter& writer,
                                         const UniqueTrackedOptimizations& unique)
 {
     // Write the header, which is the range that this whole run encompasses.
-    JitSpew(JitSpew_OptimizationTracking, "     Header: [%" PRIuSIZE ", %" PRIuSIZE "]",
+    JitSpew(JitSpew_OptimizationTracking, "     Header: [%u, %u]",
             start->startOffset.offset(), (end - 1)->endOffset.offset());
     writer.writeUnsigned(start->startOffset.offset());
     writer.writeUnsigned((end - 1)->endOffset.offset());
 
     // Write the first entry of the run, which is not delta-encoded.
     JitSpew(JitSpew_OptimizationTracking,
-            "     [%6" PRIuSIZE ", %6" PRIuSIZE "]                        vector %3u, offset %4" PRIuSIZE,
+            "     [%6u, %6u]                        vector %3u, offset %4u",
             start->startOffset.offset(), start->endOffset.offset(),
             unique.indexOf(start->optimizations), writer.length());
     uint32_t prevEndOffset = start->endOffset.offset();
@@ -789,7 +789,7 @@ IonTrackedOptimizationsRegion::WriteRun(CompactBufferWriter& writer,
         uint8_t index = unique.indexOf(entry->optimizations);
 
         JitSpew(JitSpew_OptimizationTracking,
-                "     [%6u, %6u] delta [+%5u, +%5u] vector %3u, offset %4" PRIuSIZE,
+                "     [%6u, %6u] delta [+%5u, +%5u] vector %3u, offset %4u",
                 startOffset, endOffset, startDelta, length, index, writer.length());
 
         WriteDelta(writer, startDelta, length, index);
@@ -825,7 +825,7 @@ WriteOffsetsTable(CompactBufferWriter& writer, const Vector<uint32_t, 16>& offse
 
     // Write entry offset table.
     for (size_t i = 0; i < offsets.length(); i++) {
-        JitSpew(JitSpew_OptimizationTracking, "   Entry %" PRIuSIZE " reverse offset %u",
+        JitSpew(JitSpew_OptimizationTracking, "   Entry %u reverse offset %u",
                 i, tableOffset - padding - offsets[i]);
         writer.writeNativeEndianUint32_t(tableOffset - padding - offsets[i]);
     }
@@ -919,7 +919,7 @@ jit::WriteIonTrackedOptimizationsTable(JSContext* cx, CompactBufferWriter& write
     if (JitSpewEnabled(JitSpew_OptimizationTracking)) {
         JitSpewStart(JitSpew_OptimizationTracking, "=> Training data: ");
         for (const NativeToTrackedOptimizations* entry = start; entry != end; entry++) {
-            JitSpewCont(JitSpew_OptimizationTracking, "%" PRIuSIZE ",%" PRIuSIZE ",%u ",
+            JitSpewCont(JitSpew_OptimizationTracking, "%u,%u,%u ",
                         entry->startOffset.offset(), entry->endOffset.offset(),
                         unique.indexOf(entry->optimizations));
         }
@@ -934,8 +934,7 @@ jit::WriteIonTrackedOptimizationsTable(JSContext* cx, CompactBufferWriter& write
     JitSpew(JitSpew_Profiling, "=> Writing regions");
     while (entry != end) {
         uint32_t runLength = IonTrackedOptimizationsRegion::ExpectedRunLength(entry, end);
-        JitSpew(JitSpew_OptimizationTracking,
-                "   Run at entry %" PRIuSIZE ", length %" PRIu32 ", offset %" PRIuSIZE,
+        JitSpew(JitSpew_OptimizationTracking, "   Run at entry %u, length %u, offset %u",
                 entry - start, runLength, writer.length());
 
         if (!offsets.append(writer.length()))
@@ -958,7 +957,7 @@ jit::WriteIonTrackedOptimizationsTable(JSContext* cx, CompactBufferWriter& write
     offsets.clear();
 
     const UniqueTrackedOptimizations::SortedVector& vec = unique.sortedVector();
-    JitSpew(JitSpew_OptimizationTracking, "=> Writing unique optimizations table with %" PRIuSIZE " entr%s",
+    JitSpew(JitSpew_OptimizationTracking, "=> Writing unique optimizations table with %u entr%s",
             vec.length(), vec.length() == 1 ? "y" : "ies");
 
     // Write out type info payloads.
@@ -968,8 +967,7 @@ jit::WriteIonTrackedOptimizationsTable(JSContext* cx, CompactBufferWriter& write
 
     for (const UniqueTrackedOptimizations::SortEntry* p = vec.begin(); p != vec.end(); p++) {
         const TempOptimizationTypeInfoVector* v = p->types;
-        JitSpew(JitSpew_OptimizationTracking,
-                "   Type info entry %" PRIuSIZE " of length %" PRIuSIZE ", offset %" PRIuSIZE,
+        JitSpew(JitSpew_OptimizationTracking, "   Type info entry %u of length %u, offset %u",
                 p - vec.begin(), v->length(), writer.length());
         SpewTempOptimizationTypeInfoVector(v, "  ");
 
@@ -1019,8 +1017,7 @@ jit::WriteIonTrackedOptimizationsTable(JSContext* cx, CompactBufferWriter& write
     // Write out attempts payloads.
     for (const UniqueTrackedOptimizations::SortEntry* p = vec.begin(); p != vec.end(); p++) {
         const TempOptimizationAttemptsVector* v = p->attempts;
-        JitSpew(JitSpew_OptimizationTracking,
-                "   Attempts entry %" PRIuSIZE " of length %" PRIuSIZE ", offset %" PRIuSIZE,
+        JitSpew(JitSpew_OptimizationTracking, "   Attempts entry %u of length %u, offset %u",
                 p - vec.begin(), v->length(), writer.length());
         SpewTempOptimizationAttemptsVector(v, "  ");
 
diff --git a/js/src/jit/Recover.cpp b/js/src/jit/Recover.cpp
index 93b2c2390a3d..73f4393806eb 100644
--- a/js/src/jit/Recover.cpp
+++ b/js/src/jit/Recover.cpp
@@ -6,8 +6,6 @@
 
 #include "jit/Recover.h"
 
-#include "mozilla/SizePrintfMacros.h"
-
 #include "jsapi.h"
 #include "jscntxt.h"
 #include "jsmath.h"
@@ -125,7 +123,7 @@ MResumePoint::writeRecoverData(CompactBufferWriter& writer) const
     uint32_t formalArgs = CountArgSlots(script, fun);
     uint32_t nallocs = formalArgs + script->nfixed() + exprStack;
 
-    JitSpew(JitSpew_IonSnapshots, "Starting frame; implicit %u, formals %u, fixed %" PRIuSIZE ", exprs %u",
+    JitSpew(JitSpew_IonSnapshots, "Starting frame; implicit %u, formals %u, fixed %u, exprs %u",
             implicit, formalArgs - implicit, script->nfixed(), exprStack);
 
     uint32_t pcoff = script->pcToOffset(pc());
diff --git a/js/src/jit/Safepoints.cpp b/js/src/jit/Safepoints.cpp
index b0bb530f9933..c775c7d131c0 100644
--- a/js/src/jit/Safepoints.cpp
+++ b/js/src/jit/Safepoints.cpp
@@ -7,7 +7,6 @@
 #include "jit/Safepoints.h"
 
 #include "mozilla/MathAlgorithms.h"
-#include "mozilla/SizePrintfMacros.h"
 
 #include "jit/BitSet.h"
 #include "jit/JitSpewer.h"
@@ -32,7 +31,7 @@ SafepointWriter::init(TempAllocator& alloc)
 uint32_t
 SafepointWriter::startEntry()
 {
-    JitSpew(JitSpew_Safepoints, "Encoding safepoint (position %" PRIuSIZE "):", stream_.length());
+    JitSpew(JitSpew_Safepoints, "Encoding safepoint (position %d):", stream_.length());
     return uint32_t(stream_.length());
 }
 
diff --git a/js/src/jit/SharedIC.cpp b/js/src/jit/SharedIC.cpp
index 177f5e8e394e..1c227439e349 100644
--- a/js/src/jit/SharedIC.cpp
+++ b/js/src/jit/SharedIC.cpp
@@ -2132,7 +2132,7 @@ UpdateExistingGenerationalDOMProxyStub(ICGetProp_Fallback* stub,
                 // Update generation
                 uint64_t generation = expandoAndGeneration->generation;
                 JitSpew(JitSpew_BaselineIC,
-                        "  Updating existing stub with generation, old value: %" PRIu64 ", "
+                        "  Updating existing stub with generation, old value: %i, "
                         "new value: %" PRIu64 "", updateStub->generation(),
                         generation);
                 updateStub->setGeneration(generation);
diff --git a/js/src/jit/SharedIC.h b/js/src/jit/SharedIC.h
index 42198c89096f..b8e081688897 100644
--- a/js/src/jit/SharedIC.h
+++ b/js/src/jit/SharedIC.h
@@ -202,10 +202,8 @@ class ICFallbackStub;
 #undef FORWARD_DECLARE_STUBS
 
 #ifdef JS_JITSPEW
-void FallbackICSpew(JSContext* cx, ICFallbackStub* stub, const char* fmt, ...)
-    MOZ_FORMAT_PRINTF(3, 4);
-void TypeFallbackICSpew(JSContext* cx, ICTypeMonitor_Fallback* stub, const char* fmt, ...)
-    MOZ_FORMAT_PRINTF(3, 4);
+void FallbackICSpew(JSContext* cx, ICFallbackStub* stub, const char* fmt, ...);
+void TypeFallbackICSpew(JSContext* cx, ICTypeMonitor_Fallback* stub, const char* fmt, ...);
 #else
 #define FallbackICSpew(...)
 #define TypeFallbackICSpew(...)
diff --git a/js/src/jit/ValueNumbering.cpp b/js/src/jit/ValueNumbering.cpp
index 8d563f8ef909..e8b245274bfe 100644
--- a/js/src/jit/ValueNumbering.cpp
+++ b/js/src/jit/ValueNumbering.cpp
@@ -996,7 +996,7 @@ ValueNumberer::visitBlock(MBasicBlock* block, const MBasicBlock* dominatorRoot)
 bool
 ValueNumberer::visitDominatorTree(MBasicBlock* dominatorRoot)
 {
-    JitSpew(JitSpew_GVN, "  Visiting dominator tree (with %" PRIu64 " blocks) rooted at block%u%s",
+    JitSpew(JitSpew_GVN, "  Visiting dominator tree (with %llu blocks) rooted at block%u%s",
             uint64_t(dominatorRoot->numDominated()), dominatorRoot->id(),
             dominatorRoot == graph_.entryBlock() ? " (normal entry block)" :
             dominatorRoot == graph_.osrBlock() ? " (OSR entry block)" :
@@ -1222,7 +1222,7 @@ ValueNumberer::run(UpdateAliasAnalysisFlag updateAliasAnalysis)
 {
     updateAliasAnalysis_ = updateAliasAnalysis == UpdateAliasAnalysis;
 
-    JitSpew(JitSpew_GVN, "Running GVN on graph (with %" PRIu64 " blocks)",
+    JitSpew(JitSpew_GVN, "Running GVN on graph (with %llu blocks)",
             uint64_t(graph_.numBlocks()));
 
     // Adding fixup blocks only make sense iff we have a second entry point into
@@ -1282,7 +1282,7 @@ ValueNumberer::run(UpdateAliasAnalysisFlag updateAliasAnalysis)
             break;
         }
 
-        JitSpew(JitSpew_GVN, "Re-running GVN on graph (run %d, now with %" PRIu64 " blocks)",
+        JitSpew(JitSpew_GVN, "Re-running GVN on graph (run %d, now with %llu blocks)",
                 runs, uint64_t(graph_.numBlocks()));
     }
 
diff --git a/js/src/jit/arm/Assembler-arm.h b/js/src/jit/arm/Assembler-arm.h
index 04813096c044..455a3e828515 100644
--- a/js/src/jit/arm/Assembler-arm.h
+++ b/js/src/jit/arm/Assembler-arm.h
@@ -1363,7 +1363,7 @@ class Assembler : public AssemblerShared
     uint32_t spewResolve(Label* l);
     uint32_t spewProbe(Label* l);
     uint32_t spewDefine(Label* l);
-    void spew(const char* fmt, ...) MOZ_FORMAT_PRINTF(2, 3);
+    void spew(const char* fmt, ...);
     void spew(const char* fmt, va_list args);
 #endif
 
diff --git a/js/src/jit/arm/disasm/Disasm-arm.cpp b/js/src/jit/arm/disasm/Disasm-arm.cpp
index 8bd7bff0c283..1e0cb389387b 100644
--- a/js/src/jit/arm/disasm/Disasm-arm.cpp
+++ b/js/src/jit/arm/disasm/Disasm-arm.cpp
@@ -43,7 +43,6 @@ namespace disasm {
 
 // Helper function for printing to a Vector.
 static int
-MOZ_FORMAT_PRINTF(2, 3)
 SNPrintF(V8Vector<char> str, const char* format, ...)
 {
     va_list args;
diff --git a/js/src/jit/shared/CodeGenerator-shared.cpp b/js/src/jit/shared/CodeGenerator-shared.cpp
index f69cb7449196..30c638edc375 100644
--- a/js/src/jit/shared/CodeGenerator-shared.cpp
+++ b/js/src/jit/shared/CodeGenerator-shared.cpp
@@ -7,7 +7,6 @@
 #include "jit/shared/CodeGenerator-shared-inl.h"
 
 #include "mozilla/DebugOnly.h"
-#include "mozilla/SizePrintfMacros.h"
 
 #include "jit/CompactBuffer.h"
 #include "jit/IonCaches.h"
@@ -234,7 +233,7 @@ CodeGeneratorShared::addNativeToBytecodeEntry(const BytecodeSite* site)
         // bytecodeOffset, but the nativeOffset has changed, do nothing.
         // The same site just generated some more code.
         if (lastEntry.tree == tree && lastEntry.pc == pc) {
-            JitSpew(JitSpew_Profiling, " => In-place update [%" PRIuSIZE "-%" PRIu32 "]",
+            JitSpew(JitSpew_Profiling, " => In-place update [%u-%u]",
                     lastEntry.nativeOffset.offset(), nativeOffset);
             return true;
         }
@@ -281,7 +280,7 @@ CodeGeneratorShared::dumpNativeToBytecodeEntries()
 {
 #ifdef JS_JITSPEW
     InlineScriptTree* topTree = gen->info().inlineScriptTree();
-    JitSpewStart(JitSpew_Profiling, "Native To Bytecode Entries for %s:%" PRIuSIZE "\n",
+    JitSpewStart(JitSpew_Profiling, "Native To Bytecode Entries for %s:%d\n",
                  topTree->script()->filename(), topTree->script()->lineno());
     for (unsigned i = 0; i < nativeToBytecodeList_.length(); i++)
         dumpNativeToBytecodeEntry(i);
@@ -304,16 +303,16 @@ CodeGeneratorShared::dumpNativeToBytecodeEntry(uint32_t idx)
         if (nextRef->tree == ref.tree)
             pcDelta = nextRef->pc - ref.pc;
     }
-    JitSpewStart(JitSpew_Profiling, "    %08" PRIxSIZE " [+%-6d] => %-6ld [%-4d] {%-10s} (%s:%" PRIuSIZE,
+    JitSpewStart(JitSpew_Profiling, "    %08x [+%-6d] => %-6d [%-4d] {%-10s} (%s:%d",
                  ref.nativeOffset.offset(),
                  nativeDelta,
-                 (long) (ref.pc - script->code()),
+                 ref.pc - script->code(),
                  pcDelta,
                  CodeName[JSOp(*ref.pc)],
                  script->filename(), script->lineno());
 
     for (tree = tree->caller(); tree; tree = tree->caller()) {
-        JitSpewCont(JitSpew_Profiling, " <= %s:%" PRIuSIZE, tree->script()->filename(),
+        JitSpewCont(JitSpew_Profiling, " <= %s:%d", tree->script()->filename(),
                                                     tree->script()->lineno());
     }
     JitSpewCont(JitSpew_Profiling, ")");
@@ -928,7 +927,7 @@ CodeGeneratorShared::generateCompactTrackedOptimizationsMap(JSContext* cx, JitCo
             "== Compact Native To Optimizations Map [%p-%p] size %u",
             data, data + trackedOptimizationsMapSize_, trackedOptimizationsMapSize_);
     JitSpew(JitSpew_OptimizationTracking,
-            "     with type list of length %" PRIuSIZE ", size %" PRIuSIZE,
+            "     with type list of length %u, size %u",
             allTypes->length(), allTypes->length() * sizeof(IonTrackedTypeWithAddendum));
 
     return true;
diff --git a/js/src/jit/shared/IonAssemblerBufferWithConstantPools.h b/js/src/jit/shared/IonAssemblerBufferWithConstantPools.h
index 74fa60b12402..c6783c61950a 100644
--- a/js/src/jit/shared/IonAssemblerBufferWithConstantPools.h
+++ b/js/src/jit/shared/IonAssemblerBufferWithConstantPools.h
@@ -8,7 +8,6 @@
 #define jit_shared_IonAssemblerBufferWithConstantPools_h
 
 #include "mozilla/MathAlgorithms.h"
-#include "mozilla/SizePrintfMacros.h"
 
 #include <algorithm>
 
@@ -793,7 +792,7 @@ struct AssemblerBufferWithConstantPools : public AssemblerBuffer<SliceSize, Inst
             if (numPoolEntries)
                 JitSpew(JitSpew_Pools, "[%d] Inserting pool entry caused a spill", id);
             else
-                JitSpew(JitSpew_Pools, "[%d] Inserting instruction(%" PRIuSIZE ") caused a spill", id,
+                JitSpew(JitSpew_Pools, "[%d] Inserting instruction(%d) caused a spill", id,
                         sizeExcludingCurrentPool());
 
             finishPool();
@@ -864,7 +863,7 @@ struct AssemblerBufferWithConstantPools : public AssemblerBuffer<SliceSize, Inst
         // Now to get an instruction to write.
         PoolEntry retPE;
         if (numPoolEntries) {
-            JitSpew(JitSpew_Pools, "[%d] Entry has index %u, offset %" PRIuSIZE, id, index,
+            JitSpew(JitSpew_Pools, "[%d] Entry has index %u, offset %u", id, index,
                     sizeExcludingCurrentPool());
             Asm::InsertIndexIntoTag(inst, index);
             // Figure out the offset within the pool entries.
@@ -936,8 +935,8 @@ struct AssemblerBufferWithConstantPools : public AssemblerBuffer<SliceSize, Inst
     }
 
     void finishPool() {
-        JitSpew(JitSpew_Pools, "[%d] Attempting to finish pool %" PRIuSIZE " with %u entries.",
-                id, poolInfo_.length(), pool_.numEntries());
+        JitSpew(JitSpew_Pools, "[%d] Attempting to finish pool %d with %d entries.", id,
+                poolInfo_.length(), pool_.numEntries());
 
         if (pool_.numEntries() == 0 && !hasExpirableShortRangeBranches()) {
             // If there is no data in the pool being dumped, don't dump anything.
@@ -1005,7 +1004,7 @@ struct AssemblerBufferWithConstantPools : public AssemblerBuffer<SliceSize, Inst
             // the pool entry that is being loaded.  We need to do a non-trivial
             // amount of math here, since the pool that we've made does not
             // actually reside there in memory.
-            JitSpew(JitSpew_Pools, "[%d] Fixing entry %d offset to %" PRIuSIZE, id, idx, codeOffset);
+            JitSpew(JitSpew_Pools, "[%d] Fixing entry %d offset to %u", id, idx, codeOffset);
             Asm::PatchConstantPoolLoad(inst, (uint8_t*)inst + codeOffset);
         }
 
@@ -1038,7 +1037,7 @@ struct AssemblerBufferWithConstantPools : public AssemblerBuffer<SliceSize, Inst
         // assumed that no pool entries are allocated in a no-pool region and
         // this is asserted when allocating entries.
         if (!hasSpaceForInsts(maxInst, 0)) {
-            JitSpew(JitSpew_Pools, "[%d] No-Pool instruction(%" PRIuSIZE ") caused a spill.", id,
+            JitSpew(JitSpew_Pools, "[%d] No-Pool instruction(%d) caused a spill.", id,
                     sizeExcludingCurrentPool());
             finishPool();
         }
@@ -1078,8 +1077,8 @@ struct AssemblerBufferWithConstantPools : public AssemblerBuffer<SliceSize, Inst
         // dumped at the aligned code position.
         if (!hasSpaceForInsts(requiredFill / InstSize + 1, 0)) {
             // Alignment would cause a pool dump, so dump the pool now.
-            JitSpew(JitSpew_Pools, "[%d] Alignment of %d at %" PRIuSIZE " caused a spill.",
-                    id, alignment, sizeExcludingCurrentPool());
+            JitSpew(JitSpew_Pools, "[%d] Alignment of %d at %d caused a spill.", id, alignment,
+                    sizeExcludingCurrentPool());
             finishPool();
         }
 
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 4f2c326b16a2..5a84657edaf5 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -5199,16 +5199,13 @@ const uint16_t MaxNumErrorArguments = 10;
  * and its arguments.
  */
 extern JS_PUBLIC_API(void)
-JS_ReportErrorASCII(JSContext* cx, const char* format, ...)
-    MOZ_FORMAT_PRINTF(2, 3);
+JS_ReportErrorASCII(JSContext* cx, const char* format, ...);
 
 extern JS_PUBLIC_API(void)
-JS_ReportErrorLatin1(JSContext* cx, const char* format, ...)
-    MOZ_FORMAT_PRINTF(2, 3);
+JS_ReportErrorLatin1(JSContext* cx, const char* format, ...);
 
 extern JS_PUBLIC_API(void)
-JS_ReportErrorUTF8(JSContext* cx, const char* format, ...)
-    MOZ_FORMAT_PRINTF(2, 3);
+JS_ReportErrorUTF8(JSContext* cx, const char* format, ...);
 
 /*
  * Use an errorNumber to retrieve the format string, args are char*
@@ -5260,16 +5257,13 @@ JS_ReportErrorNumberUCArray(JSContext* cx, JSErrorCallback errorCallback,
  * being set, false otherwise.
  */
 extern JS_PUBLIC_API(bool)
-JS_ReportWarningASCII(JSContext* cx, const char* format, ...)
-    MOZ_FORMAT_PRINTF(2, 3);
+JS_ReportWarningASCII(JSContext* cx, const char* format, ...);
 
 extern JS_PUBLIC_API(bool)
-JS_ReportWarningLatin1(JSContext* cx, const char* format, ...)
-    MOZ_FORMAT_PRINTF(2, 3);
+JS_ReportWarningLatin1(JSContext* cx, const char* format, ...);
 
 extern JS_PUBLIC_API(bool)
-JS_ReportWarningUTF8(JSContext* cx, const char* format, ...)
-    MOZ_FORMAT_PRINTF(2, 3);
+JS_ReportWarningUTF8(JSContext* cx, const char* format, ...);
 
 extern JS_PUBLIC_API(bool)
 JS_ReportErrorFlagsAndNumberASCII(JSContext* cx, unsigned flags,
diff --git a/js/src/jsobj.cpp b/js/src/jsobj.cpp
index 27321c2034c1..94be4fccd103 100644
--- a/js/src/jsobj.cpp
+++ b/js/src/jsobj.cpp
@@ -3630,11 +3630,11 @@ js::DumpBacktrace(JSContext* cx, FILE* fp)
             i.isWasm() ? 'W' :
             '?';
 
-        sprinter.printf("#%" PRIuSIZE " %14p %c   %s:%d",
+        sprinter.printf("#%d %14p %c   %s:%d",
                         depth, i.rawFramePtr(), frameType, filename, line);
 
         if (i.hasScript()) {
-            sprinter.printf(" (%p @ %" PRIuSIZE ")\n",
+            sprinter.printf(" (%p @ %d)\n",
                             i.script(), i.script()->pcToOffset(i.pc()));
         } else {
             sprinter.printf(" (%p)\n", i.pc());
diff --git a/js/src/jsopcode.cpp b/js/src/jsopcode.cpp
index ff340275806e..a492b36831fa 100644
--- a/js/src/jsopcode.cpp
+++ b/js/src/jsopcode.cpp
@@ -151,14 +151,14 @@ const char * PCCounts::numExecName = "interp";
 static MOZ_MUST_USE bool
 DumpIonScriptCounts(Sprinter* sp, HandleScript script, jit::IonScriptCounts* ionCounts)
 {
-    if (!sp->jsprintf("IonScript [%" PRIuSIZE " blocks]:\n", ionCounts->numBlocks()))
+    if (!sp->jsprintf("IonScript [%lu blocks]:\n", ionCounts->numBlocks()))
         return false;
 
     for (size_t i = 0; i < ionCounts->numBlocks(); i++) {
         const jit::IonBlockCounts& block = ionCounts->block(i);
         unsigned lineNumber = 0, columnNumber = 0;
         lineNumber = PCToLineNumber(script, script->offsetToPC(block.offset()), &columnNumber);
-        if (!sp->jsprintf("BB #%" PRIu32 " [%05u,%u,%u]",
+        if (!sp->jsprintf("BB #%lu [%05u,%u,%u]",
                           block.id(), block.offset(), lineNumber, columnNumber))
         {
             return false;
@@ -168,10 +168,10 @@ DumpIonScriptCounts(Sprinter* sp, HandleScript script, jit::IonScriptCounts* ion
                 return false;
         }
         for (size_t j = 0; j < block.numSuccessors(); j++) {
-            if (!sp->jsprintf(" -> #%" PRIu32, block.successor(j)))
+            if (!sp->jsprintf(" -> #%lu", block.successor(j)))
                 return false;
         }
-        if (!sp->jsprintf(" :: %" PRIu64 " hits\n", block.hitCount()))
+        if (!sp->jsprintf(" :: %llu hits\n", block.hitCount()))
             return false;
         if (!sp->jsprintf("%s\n", block.code()))
             return false;
diff --git a/js/src/jsprf.cpp b/js/src/jsprf.cpp
index 646b938de834..1f8c1a6dffc3 100644
--- a/js/src/jsprf.cpp
+++ b/js/src/jsprf.cpp
@@ -63,18 +63,18 @@ struct NumArgState
 typedef mozilla::Vector<NumArgState, 20, js::SystemAllocPolicy> NumArgStateVector;
 
 
-#define TYPE_SHORT      0
-#define TYPE_USHORT     1
+#define TYPE_INT16      0
+#define TYPE_UINT16     1
 #define TYPE_INTN       2
 #define TYPE_UINTN      3
-#define TYPE_LONG       4
-#define TYPE_ULONG      5
-#define TYPE_LONGLONG   6
-#define TYPE_ULONGLONG  7
+#define TYPE_INT32      4
+#define TYPE_UINT32     5
+#define TYPE_INT64      6
+#define TYPE_UINT64     7
 #define TYPE_STRING     8
 #define TYPE_DOUBLE     9
 #define TYPE_INTSTR     10
-#define TYPE_POINTER    11
+#define TYPE_WSTRING    11
 #define TYPE_UNKNOWN    20
 
 #define FLAG_LEFT       0x1
@@ -89,9 +89,31 @@ generic_write(SprintfState* ss, const char* src, size_t srclen)
     return (*ss->stuff)(ss, src, srclen);
 }
 
+inline bool
+generic_write(SprintfState* ss, const char16_t* src, size_t srclen)
+{
+    const size_t CHUNK_SIZE = 64;
+    char chunk[CHUNK_SIZE];
+
+    size_t j = 0;
+    size_t i = 0;
+    while (i < srclen) {
+        // FIXME: truncates characters to 8 bits
+        chunk[j++] = char(src[i++]);
+
+        if (j == CHUNK_SIZE || i == srclen) {
+            if (!(*ss->stuff)(ss, chunk, j))
+                return false;
+            j = 0;
+        }
+    }
+    return true;
+}
+
 // Fill into the buffer using the data in src
+template <typename Char>
 static bool
-fill2(SprintfState* ss, const char* src, int srclen, int width, int flags)
+fill2(SprintfState* ss, const Char* src, int srclen, int width, int flags)
 {
     char space = ' ';
 
@@ -296,16 +318,19 @@ static bool cvt_f(SprintfState* ss, double d, const char* fmt0, const char* fmt1
 }
 
 static inline const char* generic_null_str(const char*) { return "(null)"; }
+static inline const char16_t* generic_null_str(const char16_t*) { return u"(null)"; }
 
 static inline size_t generic_strlen(const char* s) { return strlen(s); }
+static inline size_t generic_strlen(const char16_t* s) { return js_strlen(s); }
 
 /*
  * Convert a string into its printable form.  "width" is the output
  * width. "prec" is the maximum number of characters of "s" to output,
  * where -1 means until NUL.
  */
+template <typename Char>
 static bool
-cvt_s(SprintfState* ss, const char* s, int width, int prec, int flags)
+cvt_s(SprintfState* ss, const Char* s, int width, int prec, int flags)
 {
     if (prec == 0)
         return true;
@@ -427,24 +452,23 @@ BuildArgArray(const char* fmt, va_list ap, NumArgStateVector& nas)
         // size
         nas[cn].type = TYPE_INTN;
         if (c == 'h') {
-            nas[cn].type = TYPE_SHORT;
+            nas[cn].type = TYPE_INT16;
             c = *p++;
         } else if (c == 'L') {
-            nas[cn].type = TYPE_LONGLONG;
+            // XXX not quite sure here
+            nas[cn].type = TYPE_INT64;
             c = *p++;
         } else if (c == 'l') {
-            nas[cn].type = TYPE_LONG;
+            nas[cn].type = TYPE_INT32;
             c = *p++;
             if (c == 'l') {
-                nas[cn].type = TYPE_LONGLONG;
+                nas[cn].type = TYPE_INT64;
                 c = *p++;
             }
         } else if (c == 'z' || c == 'I') {
-            static_assert(sizeof(size_t) == sizeof(int) || sizeof(size_t) == sizeof(long) ||
-                          sizeof(size_t) == sizeof(long long),
+            static_assert(sizeof(size_t) == sizeof(int32_t) || sizeof(size_t) == sizeof(int64_t),
                           "size_t is not one of the expected sizes");
-            nas[cn].type = sizeof(size_t) == sizeof(int) ? TYPE_INTN :
-                sizeof(size_t) == sizeof(long) ? TYPE_LONG : TYPE_LONGLONG;
+            nas[cn].type = sizeof(size_t) == sizeof(int64_t) ? TYPE_INT64 : TYPE_INT32;
             c = *p++;
         }
 
@@ -466,7 +490,16 @@ BuildArgArray(const char* fmt, va_list ap, NumArgStateVector& nas)
             break;
 
         case 'p':
-            nas[cn].type = TYPE_POINTER;
+            // XXX should use cpp
+            if (sizeof(void*) == sizeof(int32_t)) {
+                nas[cn].type = TYPE_UINT32;
+            } else if (sizeof(void*) == sizeof(int64_t)) {
+                nas[cn].type = TYPE_UINT64;
+            } else if (sizeof(void*) == sizeof(int)) {
+                nas[cn].type = TYPE_UINTN;
+            } else {
+                nas[cn].type = TYPE_UNKNOWN;
+            }
             break;
 
         case 'C':
@@ -479,7 +512,7 @@ BuildArgArray(const char* fmt, va_list ap, NumArgStateVector& nas)
             break;
 
         case 's':
-            nas[cn].type = TYPE_STRING;
+            nas[cn].type = (nas[cn].type == TYPE_UINT16) ? TYPE_WSTRING : TYPE_STRING;
             break;
 
         case 'n':
@@ -511,18 +544,18 @@ BuildArgArray(const char* fmt, va_list ap, NumArgStateVector& nas)
         VARARGS_ASSIGN(nas[cn].ap, ap);
 
         switch (nas[cn].type) {
-        case TYPE_SHORT:
-        case TYPE_USHORT:
+        case TYPE_INT16:
+        case TYPE_UINT16:
         case TYPE_INTN:
         case TYPE_UINTN:        (void) va_arg(ap, int);         break;
-        case TYPE_LONG:         (void) va_arg(ap, long);        break;
-        case TYPE_ULONG:        (void) va_arg(ap, unsigned long); break;
-        case TYPE_LONGLONG:     (void) va_arg(ap, long long);   break;
-        case TYPE_ULONGLONG:    (void) va_arg(ap, unsigned long long); break;
+        case TYPE_INT32:        (void) va_arg(ap, int32_t);     break;
+        case TYPE_UINT32:       (void) va_arg(ap, uint32_t);    break;
+        case TYPE_INT64:        (void) va_arg(ap, int64_t);     break;
+        case TYPE_UINT64:       (void) va_arg(ap, uint64_t);    break;
         case TYPE_STRING:       (void) va_arg(ap, char*);       break;
+        case TYPE_WSTRING:      (void) va_arg(ap, char16_t*);   break;
         case TYPE_INTSTR:       (void) va_arg(ap, int*);        break;
         case TYPE_DOUBLE:       (void) va_arg(ap, double);      break;
-        case TYPE_POINTER:      (void) va_arg(ap, void*);       break;
 
         default: MOZ_CRASH();
         }
@@ -543,13 +576,14 @@ dosprintf(SprintfState* ss, const char* fmt, va_list ap)
     int flags, width, prec, radix, type;
     union {
         char ch;
+        char16_t wch;
         int i;
         long l;
-        long long ll;
+        int64_t ll;
         double d;
         const char* s;
+        const char16_t* ws;
         int* ip;
-        void* p;
     } u;
     const char* fmt0;
     static const char hex[] = "0123456789abcdef";
@@ -651,24 +685,23 @@ dosprintf(SprintfState* ss, const char* fmt, va_list ap)
         // size
         type = TYPE_INTN;
         if (c == 'h') {
-            type = TYPE_SHORT;
+            type = TYPE_INT16;
             c = *fmt++;
         } else if (c == 'L') {
-            type = TYPE_LONGLONG;
+            // XXX not quite sure here
+            type = TYPE_INT64;
             c = *fmt++;
         } else if (c == 'l') {
-            type = TYPE_LONG;
+            type = TYPE_INT32;
             c = *fmt++;
             if (c == 'l') {
-                type = TYPE_LONGLONG;
+                type = TYPE_INT64;
                 c = *fmt++;
             }
         } else if (c == 'z' || c == 'I') {
-            static_assert(sizeof(size_t) == sizeof(int) || sizeof(size_t) == sizeof(long) ||
-                          sizeof(size_t) == sizeof(long long),
+            static_assert(sizeof(size_t) == sizeof(int32_t) || sizeof(size_t) == sizeof(int64_t),
                           "size_t is not one of the expected sizes");
-            type = sizeof(size_t) == sizeof(int) ? TYPE_INTN :
-                sizeof(size_t) == sizeof(long) ? TYPE_LONG : TYPE_LONGLONG;
+            type = sizeof(size_t) == sizeof(int64_t) ? TYPE_INT64 : TYPE_INT32;
             c = *fmt++;
         }
 
@@ -702,15 +735,15 @@ dosprintf(SprintfState* ss, const char* fmt, va_list ap)
 
           fetch_and_convert:
             switch (type) {
-              case TYPE_SHORT:
+              case TYPE_INT16:
                 u.l = va_arg(ap, int);
                 if (u.l < 0) {
                     u.l = -u.l;
                     flags |= FLAG_NEG;
                 }
                 goto do_long;
-              case TYPE_USHORT:
-                u.l = (unsigned short) va_arg(ap, unsigned int);
+              case TYPE_UINT16:
+                u.l = va_arg(ap, int) & 0xffff;
                 goto do_long;
               case TYPE_INTN:
                 u.l = va_arg(ap, int);
@@ -723,33 +756,30 @@ dosprintf(SprintfState* ss, const char* fmt, va_list ap)
                 u.l = (long)va_arg(ap, unsigned int);
                 goto do_long;
 
-              case TYPE_LONG:
-                u.l = va_arg(ap, long);
+              case TYPE_INT32:
+                u.l = va_arg(ap, int32_t);
                 if (u.l < 0) {
                     u.l = -u.l;
                     flags |= FLAG_NEG;
                 }
                 goto do_long;
-              case TYPE_ULONG:
-                u.l = (long)va_arg(ap, unsigned long);
+              case TYPE_UINT32:
+                u.l = (long)va_arg(ap, uint32_t);
               do_long:
                 if (!cvt_l(ss, u.l, width, prec, radix, type, flags, hexp))
                     return false;
 
                 break;
 
-              case TYPE_LONGLONG:
-                u.ll = va_arg(ap, long long);
+              case TYPE_INT64:
+                u.ll = va_arg(ap, int64_t);
                 if (u.ll < 0) {
                     u.ll = -u.ll;
                     flags |= FLAG_NEG;
                 }
                 goto do_longlong;
-              case TYPE_POINTER:
-                u.ll = (uintptr_t)va_arg(ap, void*);
-                goto do_longlong;
-              case TYPE_ULONGLONG:
-                u.ll = va_arg(ap, unsigned long long);
+              case TYPE_UINT64:
+                u.ll = va_arg(ap, uint64_t);
               do_longlong:
                 if (!cvt_ll(ss, u.ll, width, prec, radix, type, flags, hexp))
                     return false;
@@ -786,7 +816,7 @@ dosprintf(SprintfState* ss, const char* fmt, va_list ap)
                 }
             }
             switch (type) {
-              case TYPE_SHORT:
+              case TYPE_INT16:
               case TYPE_INTN:
                 u.ch = va_arg(ap, int);
                 if (!(*ss->stuff)(ss, &u.ch, 1))
@@ -802,7 +832,16 @@ dosprintf(SprintfState* ss, const char* fmt, va_list ap)
             break;
 
           case 'p':
-            type = TYPE_POINTER;
+            if (sizeof(void*) == sizeof(int32_t)) {
+                type = TYPE_UINT32;
+            } else if (sizeof(void*) == sizeof(int64_t)) {
+                type = TYPE_UINT64;
+            } else if (sizeof(void*) == sizeof(int)) {
+                type = TYPE_UINTN;
+            } else {
+                MOZ_ASSERT(0);
+                break;
+            }
             radix = 16;
             goto fetch_and_convert;
 
@@ -817,9 +856,15 @@ dosprintf(SprintfState* ss, const char* fmt, va_list ap)
 #endif
 
           case 's':
-            u.s = va_arg(ap, const char*);
-            if (!cvt_s(ss, u.s, width, prec, flags))
-                return false;
+            if(type == TYPE_INT16) {
+                u.ws = va_arg(ap, const char16_t*);
+                if (!cvt_s(ss, u.ws, width, prec, flags))
+                    return false;
+            } else {
+                u.s = va_arg(ap, const char*);
+                if (!cvt_s(ss, u.s, width, prec, flags))
+                    return false;
+            }
             break;
 
           case 'n':
@@ -959,18 +1004,18 @@ JS_vsprintf_append(char* last, const char* fmt, va_list ap)
     return ss.base;
 }
 
-#undef TYPE_SHORT
-#undef TYPE_USHORT
+#undef TYPE_INT16
+#undef TYPE_UINT16
 #undef TYPE_INTN
 #undef TYPE_UINTN
-#undef TYPE_LONG
-#undef TYPE_ULONG
-#undef TYPE_LONGLONG
-#undef TYPE_ULONGLONG
+#undef TYPE_INT32
+#undef TYPE_UINT32
+#undef TYPE_INT64
+#undef TYPE_UINT64
 #undef TYPE_STRING
 #undef TYPE_DOUBLE
 #undef TYPE_INTSTR
-#undef TYPE_POINTER
+#undef TYPE_WSTRING
 #undef TYPE_UNKNOWN
 
 #undef FLAG_LEFT
diff --git a/js/src/jsprf.h b/js/src/jsprf.h
index b84b5a5c9864..3bdbe638472c 100644
--- a/js/src/jsprf.h
+++ b/js/src/jsprf.h
@@ -14,13 +14,11 @@
 **      %x - unsigned hex
 **      %X - unsigned uppercase hex
 **      %o - unsigned octal
-**      %hd, %hu, %hx, %hX, %ho - "short" versions of above
-**      %ld, %lu, %lx, %lX, %lo - "long" versions of above
-**      %lld, %llu, %llx, %llX, %llo - "long long" versions of above
-**      %zd, %zo, %zu, %zx, %zX - size_t versions of above
-**      %Id, %Io, %Iu, %Ix, %IX - size_t versions of above (for Windows compat)
-**           You should use PRI*SIZE macros instead
-**      %s - string
+**      %hd, %hu, %hx, %hX, %ho - 16-bit versions of above
+**      %ld, %lu, %lx, %lX, %lo - 32-bit versions of above
+**      %lld, %llu, %llx, %llX, %llo - 64 bit versions of above
+**      %s - ascii string
+**      %hs - ucs2 string
 **      %c - character
 **      %p - pointer (deals with machine dependent pointer size)
 **      %f - float
@@ -39,8 +37,7 @@
 ** buffer on success, nullptr on failure. Call "JS_smprintf_free" to release
 ** the memory returned.
 */
-extern JS_PUBLIC_API(char*) JS_smprintf(const char* fmt, ...)
-    MOZ_FORMAT_PRINTF(1, 2);
+extern JS_PUBLIC_API(char*) JS_smprintf(const char* fmt, ...);
 
 /*
 ** Free the memory allocated, for the caller, by JS_smprintf
@@ -54,8 +51,7 @@ extern JS_PUBLIC_API(void) JS_smprintf_free(char* mem);
 ** will allocate the initial string. The return value is the new value of
 ** last for subsequent calls, or nullptr if there is a malloc failure.
 */
-extern JS_PUBLIC_API(char*) JS_sprintf_append(char* last, const char* fmt, ...)
-    MOZ_FORMAT_PRINTF(2, 3);
+extern JS_PUBLIC_API(char*) JS_sprintf_append(char* last, const char* fmt, ...);
 
 /*
 ** va_list forms of the above.
diff --git a/js/src/moz.build b/js/src/moz.build
index a0b563b9e4e6..8f830f6caebc 100644
--- a/js/src/moz.build
+++ b/js/src/moz.build
@@ -783,7 +783,7 @@ if CONFIG['JS_HAS_CTYPES']:
         DEFINES['FFI_BUILDING'] = True
 
 if CONFIG['GNU_CXX']:
-    CXXFLAGS += ['-Wno-shadow', '-Werror=format']
+    CXXFLAGS += ['-Wno-shadow']
 
 # Suppress warnings in third-party code.
 if CONFIG['CLANG_CXX']:
diff --git a/js/src/shell/js.cpp b/js/src/shell/js.cpp
index e120b17c293c..b53af7be407e 100644
--- a/js/src/shell/js.cpp
+++ b/js/src/shell/js.cpp
@@ -5232,7 +5232,7 @@ ReflectTrackedOptimizations(JSContext* cx, unsigned argc, Value* vp)
             uint8_t* addr = ion->method()->raw() + endOffset;
             entry.youngestFrameLocationAtAddr(rt, addr, &script, &pc);
 
-            if (!sp.jsprintf("{\"location\":\"%s:%" PRIuSIZE "\",\"offset\":%" PRIuSIZE ",\"index\":%u}%s",
+            if (!sp.jsprintf("{\"location\":\"%s:%u\",\"offset\":%u,\"index\":%u}%s",
                              script->filename(), script->lineno(), script->pcToOffset(pc), index,
                              iter.more() ? "," : ""))
             {
diff --git a/js/src/shell/jsoptparse.cpp b/js/src/shell/jsoptparse.cpp
index eaf4042d3bf4..5e1a3aa09fdc 100644
--- a/js/src/shell/jsoptparse.cpp
+++ b/js/src/shell/jsoptparse.cpp
@@ -264,7 +264,7 @@ OptionParser::extractValue(size_t argc, char** argv, size_t* i, char** value)
     if (eq) {
         *value = eq + 1;
         if (*value[0] == '\0')
-            return error("A value is required for option %.*s", (int) (eq - argv[*i]), argv[*i]);
+            return error("A value is required for option %.*s", eq - argv[*i], argv[*i]);
         return Okay;
     }
 
diff --git a/js/src/shell/jsoptparse.h b/js/src/shell/jsoptparse.h
index 274978130ea3..b2a24348186a 100644
--- a/js/src/shell/jsoptparse.h
+++ b/js/src/shell/jsoptparse.h
@@ -228,7 +228,7 @@ class OptionParser
     Option* findArgument(const char* name);
     const Option* findArgument(const char* name) const;
 
-    Result error(const char* fmt, ...) MOZ_FORMAT_PRINTF(2, 3);
+    Result error(const char* fmt, ...);
     Result extractValue(size_t argc, char** argv, size_t* i, char** value);
     Result handleArg(size_t argc, char** argv, size_t* i, bool* optsAllowed);
     Result handleOption(Option* opt, size_t argc, char** argv, size_t* i, bool* optsAllowed);
diff --git a/js/src/shell/moz.build b/js/src/shell/moz.build
index 72ea8145cc31..77475b241fa8 100644
--- a/js/src/shell/moz.build
+++ b/js/src/shell/moz.build
@@ -51,7 +51,7 @@ shellmoduleloader.inputs = [
 ]
 
 if CONFIG['GNU_CXX']:
-    CXXFLAGS += ['-Wno-shadow', '-Werror=format']
+    CXXFLAGS += ['-Wno-shadow']
 
 # This is intended as a temporary workaround to enable VS2015.
 if CONFIG['_MSC_VER']:
diff --git a/js/src/vm/CodeCoverage.cpp b/js/src/vm/CodeCoverage.cpp
index e7146a32a3be..280256b66eef 100644
--- a/js/src/vm/CodeCoverage.cpp
+++ b/js/src/vm/CodeCoverage.cpp
@@ -91,16 +91,16 @@ LCovSource::exportInto(GenericPrinter& out) const
 
     outFN_.exportInto(out);
     outFNDA_.exportInto(out);
-    out.printf("FNF:%" PRIuSIZE "\n", numFunctionsFound_);
-    out.printf("FNH:%" PRIuSIZE "\n", numFunctionsHit_);
+    out.printf("FNF:%d\n", numFunctionsFound_);
+    out.printf("FNH:%d\n", numFunctionsHit_);
 
     outBRDA_.exportInto(out);
-    out.printf("BRF:%" PRIuSIZE "\n", numBranchesFound_);
-    out.printf("BRH:%" PRIuSIZE "\n", numBranchesHit_);
+    out.printf("BRF:%d\n", numBranchesFound_);
+    out.printf("BRH:%d\n", numBranchesHit_);
 
     outDA_.exportInto(out);
-    out.printf("LF:%" PRIuSIZE "\n", numLinesInstrumented_);
-    out.printf("LH:%" PRIuSIZE "\n", numLinesHit_);
+    out.printf("LF:%d\n", numLinesInstrumented_);
+    out.printf("LH:%d\n", numLinesHit_);
 
     out.put("end_of_record\n");
 }
@@ -130,7 +130,7 @@ bool
 LCovSource::writeScript(JSScript* script)
 {
     numFunctionsFound_++;
-    outFN_.printf("FN:%" PRIuSIZE ",", script->lineno());
+    outFN_.printf("FN:%d,", script->lineno());
     if (!writeScriptName(outFN_, script))
         return false;
     outFN_.put("\n", 1);
@@ -191,7 +191,7 @@ LCovSource::writeScript(JSScript* script)
             }
 
             if (oldLine != lineno && fallsthrough) {
-                outDA_.printf("DA:%" PRIuSIZE ",%" PRIu64 "\n", lineno, hits);
+                outDA_.printf("DA:%d,%" PRIu64 "\n", lineno, hits);
 
                 // Count the number of lines instrumented & hit.
                 numLinesInstrumented_++;
@@ -220,13 +220,13 @@ LCovSource::writeScript(JSScript* script)
             }
 
             uint64_t taken = hits - fallthroughHits;
-            outBRDA_.printf("BRDA:%" PRIuSIZE ",%" PRIuSIZE ",0,", lineno, branchId);
+            outBRDA_.printf("BRDA:%d,%d,0,", lineno, branchId);
             if (taken)
                 outBRDA_.printf("%" PRIu64 "\n", taken);
             else
                 outBRDA_.put("-\n", 2);
 
-            outBRDA_.printf("BRDA:%" PRIuSIZE ",%" PRIuSIZE ",1,", lineno, branchId);
+            outBRDA_.printf("BRDA:%d,%d,1,", lineno, branchId);
             if (fallthroughHits)
                 outBRDA_.printf("%" PRIu64 "\n", fallthroughHits);
             else
@@ -308,8 +308,7 @@ LCovSource::writeScript(JSScript* script)
                         caseHits -= fallsThroughHits;
                     }
 
-                    outBRDA_.printf("BRDA:%" PRIuSIZE ",%" PRIuSIZE ",%" PRIuSIZE ",",
-                                    lineno, branchId, caseId);
+                    outBRDA_.printf("BRDA:%d,%d,%d,", lineno, branchId, caseId);
                     if (caseHits)
                         outBRDA_.printf("%" PRIu64 "\n", caseHits);
                     else
@@ -360,8 +359,7 @@ LCovSource::writeScript(JSScript* script)
             }
 
             if (defaultHasOwnClause) {
-                outBRDA_.printf("BRDA:%" PRIuSIZE ",%" PRIuSIZE ",%" PRIuSIZE ",",
-                                lineno, branchId, caseId);
+                outBRDA_.printf("BRDA:%d,%d,%d,", lineno, branchId, caseId);
                 if (defaultHits)
                     outBRDA_.printf("%" PRIu64 "\n", defaultHits);
                 else
diff --git a/js/src/vm/Printer.h b/js/src/vm/Printer.h
index 3ee76da44d5e..ae70d59fa114 100644
--- a/js/src/vm/Printer.h
+++ b/js/src/vm/Printer.h
@@ -43,7 +43,7 @@ class GenericPrinter
     }
 
     // Prints a formatted string into the buffer.
-    virtual int printf(const char* fmt, ...) MOZ_FORMAT_PRINTF(2, 3);
+    virtual int printf(const char* fmt, ...);
     virtual int vprintf(const char* fmt, va_list ap);
 
     // Report that a string operation failed to get the memory it requested. The
@@ -115,7 +115,7 @@ class Sprinter final : public GenericPrinter
     // Format the given format/arguments as if by JS_vsmprintf, then put it.
     // Return true on success, else return false and report an error (typically
     // OOM).
-    MOZ_MUST_USE bool jsprintf(const char* fmt, ...) MOZ_FORMAT_PRINTF(2, 3);
+    MOZ_MUST_USE bool jsprintf(const char* fmt, ...);
 
     // Prints a formatted string into the buffer.
     virtual int vprintf(const char* fmt, va_list ap) override;
@@ -157,7 +157,7 @@ class Fprinter final : public GenericPrinter
     using GenericPrinter::put; // pick up |inline int put(const char* s);|
 
     // Prints a formatted string into the buffer.
-    virtual int printf(const char* fmt, ...) override MOZ_FORMAT_PRINTF(2, 3);
+    virtual int printf(const char* fmt, ...) override;
     virtual int vprintf(const char* fmt, va_list ap) override;
 };
 
@@ -203,7 +203,7 @@ class LSprinter final : public GenericPrinter
     using GenericPrinter::put; // pick up |inline int put(const char* s);|
 
     // Prints a formatted string into the buffer.
-    virtual int printf(const char* fmt, ...) override MOZ_FORMAT_PRINTF(2, 3);
+    virtual int printf(const char* fmt, ...) override;
     virtual int vprintf(const char* fmt, va_list ap) override;
 
     // Report that a string operation failed to get the memory it requested. The
diff --git a/js/src/vm/TraceLoggingGraph.cpp b/js/src/vm/TraceLoggingGraph.cpp
index 6f6792e98040..16d270b7e54a 100644
--- a/js/src/vm/TraceLoggingGraph.cpp
+++ b/js/src/vm/TraceLoggingGraph.cpp
@@ -50,7 +50,6 @@ TraceLoggerGraphState* traceLoggerGraphState = nullptr;
 // are allowed, with %u standing for a full 32-bit number and %d standing for
 // an up to 3-digit number.
 static js::UniqueChars
-MOZ_FORMAT_PRINTF(1, 2)
 AllocTraceLogFilename(const char* pattern, ...) {
     js::UniqueChars filename;
 
diff --git a/js/src/vm/TypeInference.cpp b/js/src/vm/TypeInference.cpp
index 762edf71d3a5..97a92fccee95 100644
--- a/js/src/vm/TypeInference.cpp
+++ b/js/src/vm/TypeInference.cpp
@@ -237,7 +237,6 @@ js::InferSpewImpl(const char* fmt, ...)
 #endif
 
 MOZ_NORETURN MOZ_COLD static void
-MOZ_FORMAT_PRINTF(2, 3)
 TypeFailure(JSContext* cx, const char* fmt, ...)
 {
     char msgbuf[1024]; /* Larger error messages will be truncated */
@@ -3289,7 +3288,7 @@ js::TypeMonitorResult(JSContext* cx, JSScript* script, jsbytecode* pc, TypeSet::
     if (types->hasType(type))
         return;
 
-    InferSpew(ISpewOps, "bytecodeType: %p %05" PRIuSIZE ": %s",
+    InferSpew(ISpewOps, "bytecodeType: %p %05u: %s",
               script, script->pcToOffset(pc), TypeSet::TypeString(type));
     types->addType(cx, type);
 }
diff --git a/js/src/vm/TypeInference.h b/js/src/vm/TypeInference.h
index 26522727c98f..ee243bf299f0 100644
--- a/js/src/vm/TypeInference.h
+++ b/js/src/vm/TypeInference.h
@@ -1296,7 +1296,7 @@ const char * InferSpewColor(TypeConstraint* constraint);
 const char * InferSpewColor(TypeSet* types);
 
 #define InferSpew(channel, ...) if (InferSpewActive(channel)) { InferSpewImpl(__VA_ARGS__); } else {}
-void InferSpewImpl(const char* fmt, ...) MOZ_FORMAT_PRINTF(1, 2);
+void InferSpewImpl(const char* fmt, ...);
 
 /* Check that the type property for id in group contains value. */
 bool ObjectGroupHasProperty(JSContext* cx, ObjectGroup* group, jsid id, const Value& value);
diff --git a/js/xpconnect/loader/mozJSComponentLoader.cpp b/js/xpconnect/loader/mozJSComponentLoader.cpp
index 95c214867758..2f0c0ff40a56 100644
--- a/js/xpconnect/loader/mozJSComponentLoader.cpp
+++ b/js/xpconnect/loader/mozJSComponentLoader.cpp
@@ -154,7 +154,6 @@ private:
 };
 
 static nsresult
-MOZ_FORMAT_PRINTF(2, 3)
 ReportOnCallerUTF8(JSContext* callerContext,
                    const char* format, ...) {
     if (!callerContext) {
@@ -178,7 +177,6 @@ ReportOnCallerUTF8(JSContext* callerContext,
 }
 
 static nsresult
-MOZ_FORMAT_PRINTF(2, 3)
 ReportOnCallerUTF8(JSCLContextHelper& helper,
                    const char* format, ...)
 {
diff --git a/js/xpconnect/src/XPCThrower.cpp b/js/xpconnect/src/XPCThrower.cpp
index 4a37e1554287..ad479b4e3eb8 100644
--- a/js/xpconnect/src/XPCThrower.cpp
+++ b/js/xpconnect/src/XPCThrower.cpp
@@ -116,9 +116,9 @@ XPCThrower::ThrowBadResult(nsresult rv, nsresult result, XPCCallContext& ccx)
         format = "";
 
     if (nsXPCException::NameAndFormatForNSResult(result, &name, nullptr) && name)
-        sz = JS_smprintf("%s 0x%x (%s)", format, (unsigned) result, name);
+        sz = JS_smprintf("%s 0x%x (%s)", format, result, name);
     else
-        sz = JS_smprintf("%s 0x%x", format, (unsigned) result);
+        sz = JS_smprintf("%s 0x%x", format, result);
     NS_ENSURE_TRUE_VOID(sz);
 
     if (sz && sVerbose)
diff --git a/js/xpconnect/src/XPCWrappedJSClass.cpp b/js/xpconnect/src/XPCWrappedJSClass.cpp
index 0cf82633c6c9..518c8c94ce62 100644
--- a/js/xpconnect/src/XPCWrappedJSClass.cpp
+++ b/js/xpconnect/src/XPCWrappedJSClass.cpp
@@ -971,7 +971,7 @@ nsXPCWrappedJSClass::CallMethod(nsXPCWrappedJS* wrapper, uint16_t methodIndex,
         const char* str = "IDL methods marked with [implicit_jscontext] "
                           "or [optional_argc] may not be implemented in JS";
         // Throw and warn for good measure.
-        JS_ReportErrorASCII(cx, "%s", str);
+        JS_ReportErrorASCII(cx, str);
         NS_WARNING(str);
         return CheckForException(ccx, aes, name, GetInterfaceName());
     }
diff --git a/js/xpconnect/src/moz.build b/js/xpconnect/src/moz.build
index 94d58577cc79..9108fd66aca2 100644
--- a/js/xpconnect/src/moz.build
+++ b/js/xpconnect/src/moz.build
@@ -72,4 +72,4 @@ if CONFIG['MOZ_B2G_BT']:
     ]
 
 if CONFIG['GNU_CXX']:
-    CXXFLAGS += ['-Wno-shadow', '-Werror=format']
+    CXXFLAGS += ['-Wno-shadow']
diff --git a/js/xpconnect/wrappers/AccessCheck.cpp b/js/xpconnect/wrappers/AccessCheck.cpp
index 9f468931f197..66e96d04c34a 100644
--- a/js/xpconnect/wrappers/AccessCheck.cpp
+++ b/js/xpconnect/wrappers/AccessCheck.cpp
@@ -274,7 +274,7 @@ static void
 EnterAndThrowASCII(JSContext* cx, JSObject* wrapper, const char* msg)
 {
     JSAutoCompartment ac(cx, wrapper);
-    JS_ReportErrorASCII(cx, "%s", msg);
+    JS_ReportErrorASCII(cx, msg);
 }
 
 bool