diff --git a/netwerk/base/nsStandardURL.cpp b/netwerk/base/nsStandardURL.cpp
index e344df3165b5..9e9825f94d51 100644
--- a/netwerk/base/nsStandardURL.cpp
+++ b/netwerk/base/nsStandardURL.cpp
@@ -991,6 +991,8 @@ NS_INTERFACE_MAP_END
 NS_IMETHODIMP
 nsStandardURL::GetSpec(nsACString &result)
 {
+    MOZ_ASSERT(mSpec.Length() <= (uint32_t) net_GetURLMaxLength(),
+               "The spec should never be this long, we missed a check.");
     result = mSpec;
     return NS_OK;
 }
@@ -1279,6 +1281,10 @@ nsStandardURL::SetScheme(const nsACString &input)
         return NS_ERROR_UNEXPECTED;
     }
 
+    if (mSpec.Length() + input.Length() - Scheme().Length() > (uint32_t) net_GetURLMaxLength()) {
+        return NS_ERROR_MALFORMED_URI;
+    }
+
     InvalidateCache();
 
     int32_t shift = ReplaceSegment(mScheme.mPos, mScheme.mLen, scheme);
@@ -1316,6 +1322,10 @@ nsStandardURL::SetUserPass(const nsACString &input)
         return NS_ERROR_NOT_INITIALIZED;
     }
 
+    if (mSpec.Length() + input.Length() - Userpass(true).Length() > (uint32_t) net_GetURLMaxLength()) {
+        return NS_ERROR_MALFORMED_URI;
+    }
+
     InvalidateCache();
 
     if (userpass.IsEmpty()) {
@@ -1416,6 +1426,10 @@ nsStandardURL::SetUsername(const nsACString &input)
     if (username.IsEmpty())
         return SetUserPass(username);
 
+    if (mSpec.Length() + input.Length() - Username().Length() > (uint32_t) net_GetURLMaxLength()) {
+        return NS_ERROR_MALFORMED_URI;
+    }
+
     InvalidateCache();
 
     // escape username if necessary
@@ -1462,6 +1476,10 @@ nsStandardURL::SetPassword(const nsACString &input)
         return NS_ERROR_FAILURE;
     }
 
+    if (mSpec.Length() + input.Length() - Password().Length() > (uint32_t) net_GetURLMaxLength()) {
+        return NS_ERROR_MALFORMED_URI;
+    }
+
     InvalidateCache();
 
     if (password.IsEmpty()) {
@@ -1624,6 +1642,10 @@ nsStandardURL::SetHost(const nsACString &input)
     if (strchr(host, ' '))
         return NS_ERROR_MALFORMED_URI;
 
+    if (mSpec.Length() + strlen(host) - Host().Length() > (uint32_t) net_GetURLMaxLength()) {
+        return NS_ERROR_MALFORMED_URI;
+    }
+
     InvalidateCache();
     mHostEncoding = eEncoding_ASCII;
 
@@ -1672,7 +1694,7 @@ nsStandardURL::SetHost(const nsACString &input)
 
     return NS_OK;
 }
-             
+
 NS_IMETHODIMP
 nsStandardURL::SetPort(int32_t port)
 {
@@ -2432,6 +2454,10 @@ nsStandardURL::SetQuery(const nsACString &input)
     if (mPath.mLen < 0)
         return SetPath(flat);
 
+    if (mSpec.Length() + input.Length() - Query().Length() > (uint32_t) net_GetURLMaxLength()) {
+        return NS_ERROR_MALFORMED_URI;
+    }
+
     InvalidateCache();
 
     if (!query || !*query) {
@@ -2504,6 +2530,10 @@ nsStandardURL::SetRef(const nsACString &input)
     if (mPath.mLen < 0)
         return SetPath(flat);
 
+    if (mSpec.Length() + input.Length() - Ref().Length() > (uint32_t) net_GetURLMaxLength()) {
+        return NS_ERROR_MALFORMED_URI;
+    }
+
     InvalidateCache();
 
     if (!ref || !*ref) {
@@ -2572,6 +2602,10 @@ nsStandardURL::SetFileName(const nsACString &input)
     if (mPath.mLen < 0)
         return SetPath(flat);
 
+    if (mSpec.Length() + input.Length() - Filename().Length() > (uint32_t) net_GetURLMaxLength()) {
+        return NS_ERROR_MALFORMED_URI;
+    }
+
     int32_t shift = 0;
 
     if (!(filename && *filename)) {
@@ -2997,6 +3031,8 @@ nsStandardURL::Read(nsIObjectInputStream *stream)
 NS_IMETHODIMP
 nsStandardURL::Write(nsIObjectOutputStream *stream)
 {
+    MOZ_ASSERT(mSpec.Length() <= (uint32_t) net_GetURLMaxLength(),
+               "The spec should never be this long, we missed a check.");
     nsresult rv;
 
     rv = stream->Write32(mURLType);
@@ -3093,6 +3129,8 @@ FromIPCSegment(const mozilla::ipc::StandardURLSegment& aSegment)
 void
 nsStandardURL::Serialize(URIParams& aParams)
 {
+    MOZ_ASSERT(mSpec.Length() <= (uint32_t) net_GetURLMaxLength(),
+               "The spec should never be this long, we missed a check.");
     StandardURLParams params;
 
     params.urlType() = mURLType;
diff --git a/netwerk/test/unit/test_standardurl.js b/netwerk/test/unit/test_standardurl.js
index e30176c5666c..0d914c7d57d0 100644
--- a/netwerk/test/unit/test_standardurl.js
+++ b/netwerk/test/unit/test_standardurl.js
@@ -38,7 +38,7 @@ function pairToURLs(pair) {
   return pair.map(stringToURL);
 }
 
-function test_setEmptyPath()
+add_test(function test_setEmptyPath()
 {
   var pairs =
     [
@@ -60,9 +60,10 @@ function test_setEmptyPath()
     do_check_eq(provided.spec, target.spec);
     symmetricEquality(true, target, provided);
   }
-}
+  run_next_test();
+});
 
-function test_setQuery()
+add_test(function test_setQuery()
 {
   var pairs =
     [
@@ -99,10 +100,10 @@ function test_setQuery()
 
   do_check_eq(newProvided.spec, target.spec);
   symmetricEquality(true, newProvided, target);
+  run_next_test();
+});
 
-}
-		      
-function test_setRef()
+add_test(function test_setRef()
 {
   var tests =
     [
@@ -160,10 +161,11 @@ function test_setRef()
     a.ref = ref;
     symmetricEquality(true, a, b);
   }
-}
+  run_next_test();
+});
 
 // Bug 960014 - Make nsStandardURL::SetHost less magical around IPv6
-function test_ipv6()
+add_test(function test_ipv6()
 {
   var url = stringToURL("http://example.com");
   url.host = "[2001::1]";
@@ -180,9 +182,10 @@ function test_ipv6()
   do_check_eq(url.host, "2001");
   do_check_eq(url.port, 1);
   do_check_eq(url.hostPort, "2001:1");
-}
+  run_next_test();
+});
 
-function test_ipv6_fail()
+add_test(function test_ipv6_fail()
 {
   var url = stringToURL("http://example.com");
 
@@ -206,9 +209,10 @@ function test_ipv6_fail()
   Assert.throws(() => { url.hostPort = ""; }, "Empty hostPort should fail");
   Assert.throws(() => { url.hostPort = "[2001::1]:"; }, "missing port number");
   Assert.throws(() => { url.hostPort = "[2001::1]:bad"; }, "bad port number");
-}
+  run_next_test();
+});
 
-function test_clearedSpec()
+add_test(function test_clearedSpec()
 {
   var url = stringToURL("http://example.com/path");
   Assert.throws(() => { url.spec = "http: example"; }, "set bad spec");
@@ -218,9 +222,10 @@ function test_clearedSpec()
 
   var ref = stringToURL("http://allizom.org/path");
   symmetricEquality(true, url, ref);
-}
+  run_next_test();
+});
 
-function test_escapeBrackets()
+add_test(function test_escapeBrackets()
 {
   // Query
   var url = stringToURL("http://example.com/?a[x]=1");
@@ -241,18 +246,19 @@ function test_escapeBrackets()
 
   url = stringToURL("http://example.com/a%5Bx%5D/test");
   do_check_eq(url.spec, "http://example.com/a%5Bx%5D/test");
+  run_next_test();
+});
 
-}
-
-function test_apostropheEncoding()
+add_test(function test_apostropheEncoding()
 {
   // For now, single quote is escaped everywhere _except_ the path.
   // This policy is controlled by the bitmask in nsEscape.cpp::EscapeChars[]
   var url = stringToURL("http://example.com/dir'/file'.ext'");
   do_check_eq(url.spec, "http://example.com/dir'/file'.ext'");
-}
+  run_next_test();
+});
 
-function test_accentEncoding()
+add_test(function test_accentEncoding()
 {
   var url = stringToURL("http://example.com/?hello=`");
   do_check_eq(url.spec, "http://example.com/?hello=`");
@@ -261,9 +267,10 @@ function test_accentEncoding()
   url = stringToURL("http://example.com/?hello=%2C");
   do_check_eq(url.spec, "http://example.com/?hello=%2C");
   do_check_eq(url.query, "hello=%2C");
-}
+  run_next_test();
+});
 
-function test_percentDecoding()
+add_test(function test_percentDecoding()
 {
   var url = stringToURL("http://%70%61%73%74%65%62%69%6E.com");
   do_check_eq(url.spec, "http://pastebin.com/");
@@ -271,18 +278,25 @@ function test_percentDecoding()
   // We shouldn't unescape characters that are not allowed in the hostname.
   url = stringToURL("http://example.com%0a%23.google.com/");
   do_check_eq(url.spec, "http://example.com%0a%23.google.com/");
-}
+  run_next_test();
+});
 
-function run_test()
+add_test(function test_hugeStringThrows()
 {
-  test_setEmptyPath();
-  test_setQuery();
-  test_setRef();
-  test_ipv6();
-  test_ipv6_fail();
-  test_clearedSpec();
-  test_escapeBrackets();
-  test_apostropheEncoding();
-  test_accentEncoding();
-  test_percentDecoding();
-}
+  let prefs = Cc["@mozilla.org/preferences-service;1"]
+                .getService(Ci.nsIPrefService);
+  let maxLen = prefs.getIntPref("network.standard-url.max-length");
+  let url = stringToURL("http://test:test@example.com");
+
+  let hugeString = new Array(maxLen + 1).fill("a").join("");
+  let properties = ["spec", "scheme", "userPass", "username",
+                    "password", "hostPort", "host", "path", "ref",
+                    "query", "fileName", "filePath", "fileBaseName", "fileExtension"];
+  for (let prop of properties) {
+    Assert.throws(() => url[prop] = hugeString,
+                  /NS_ERROR_MALFORMED_URI/,
+                  `Passing a huge string to "${prop}" should throw`);
+  }
+
+  run_next_test();
+});