diff --git a/modules/libjar/moz.build b/modules/libjar/moz.build
index 8fcf043127a0..7860db80c5cd 100644
--- a/modules/libjar/moz.build
+++ b/modules/libjar/moz.build
@@ -32,16 +32,12 @@ EXPORTS += [
 ]
 
 UNIFIED_SOURCES += [
-    'nsJARProtocolHandler.cpp',
-    'nsJARURI.cpp',
-]
-
-# These files cannot be built in unified mode because they rely on plarena.h.
-SOURCES += [
     'nsJAR.cpp',
     'nsJARChannel.cpp',
     'nsJARFactory.cpp',
     'nsJARInputStream.cpp',
+    'nsJARProtocolHandler.cpp',
+    'nsJARURI.cpp',
     'nsZipArchive.cpp',
 ]
 
diff --git a/modules/libjar/nsZipArchive.cpp b/modules/libjar/nsZipArchive.cpp
index f07c42a62aad..7993ebf474c2 100644
--- a/modules/libjar/nsZipArchive.cpp
+++ b/modules/libjar/nsZipArchive.cpp
@@ -10,11 +10,6 @@
  * or pointers to it across thread boundaries.
  */
 
-// This must be the first include in the file in order for the
-// PL_ARENA_CONST_ALIGN_MASK macro to be effective.
-#define PL_ARENA_CONST_ALIGN_MASK  (sizeof(void*)-1)
-#include "plarena.h"
-
 #define READTYPE  int32_t
 #include "zlib.h"
 #include "nsISupportsUtils.h"
@@ -356,9 +351,6 @@ nsresult nsZipArchive::OpenArchive(nsZipHandle *aZipHandle, PRFileDesc *aFd)
 {
   mFd = aZipHandle;
 
-  // Initialize our arena
-  PL_INIT_ARENA_POOL(&mArena, "ZipArena", ZIP_ARENABLOCKSIZE);
-
   //-- get table of contents for archive
   nsresult rv = BuildFileList(aFd);
   if (NS_SUCCEEDED(rv)) {
@@ -427,7 +419,7 @@ nsresult nsZipArchive::Test(const char *aEntryName)
 nsresult nsZipArchive::CloseArchive()
 {
   if (mFd) {
-    PL_FinishArenaPool(&mArena);
+    mArena.Clear();
     mFd = nullptr;
   }
 
@@ -667,9 +659,7 @@ static nsresult ResolveSymlink(const char *path)
 nsZipItem* nsZipArchive::CreateZipItem()
 {
   // Arena allocate the nsZipItem
-  void *mem;
-  PL_ARENA_ALLOCATE(mem, &mArena, sizeof(nsZipItem));
-  return (nsZipItem*)mem;
+  return (nsZipItem*)mArena.Allocate(sizeof(nsZipItem));
 }
 
 //---------------------------------------------
diff --git a/modules/libjar/nsZipArchive.h b/modules/libjar/nsZipArchive.h
index 2de67903277f..373492370468 100644
--- a/modules/libjar/nsZipArchive.h
+++ b/modules/libjar/nsZipArchive.h
@@ -11,12 +11,12 @@
 #define ZIP_TABSIZE   256
 #define ZIP_BUFLEN    (4*1024)      /* Used as output buffer when deflating items to a file */
 
-#include "plarena.h"
 #include "zlib.h"
 #include "zipstruct.h"
 #include "nsAutoPtr.h"
 #include "nsIFile.h"
 #include "nsISupportsImpl.h" // For mozilla::ThreadSafeAutoRefCnt
+#include "mozilla/ArenaAllocator.h"
 #include "mozilla/FileUtils.h"
 #include "mozilla/FileLocation.h"
 #include "mozilla/UniquePtr.h"
@@ -217,7 +217,7 @@ private:
   NS_DECL_OWNINGTHREAD
 
   nsZipItem*    mFiles[ZIP_TABSIZE];
-  PLArenaPool   mArena;
+  mozilla::ArenaAllocator<1024, sizeof(void*)> mArena;
 
   const char*   mCommentPtr;
   uint16_t      mCommentLen;