diff --git a/content/base/src/nsDOMFile.cpp b/content/base/src/nsDOMFile.cpp
index b9152825616..c1f2f362614 100644
--- a/content/base/src/nsDOMFile.cpp
+++ b/content/base/src/nsDOMFile.cpp
@@ -494,7 +494,7 @@ nsDOMFileFile::GetMozFullPathInternal(nsAString &aFilename)
 NS_IMETHODIMP
 nsDOMFileFile::GetLastModifiedDate(JSContext* cx, JS::Value *aLastModifiedDate)
 {
-  int64_t msecs;
+  PRTime msecs;
   mFile->GetLastModifiedTime(&msecs);
   JSObject* date = JS_NewDateObjectMsec(cx, msecs);
   if (date) {
diff --git a/dom/devicestorage/nsDeviceStorage.cpp b/dom/devicestorage/nsDeviceStorage.cpp
index 35bb2f5d614..9b267f6ae7b 100644
--- a/dom/devicestorage/nsDeviceStorage.cpp
+++ b/dom/devicestorage/nsDeviceStorage.cpp
@@ -316,7 +316,7 @@ DeviceStorageFile::collectFilesInternal(nsTArray<nsRefPtr<DeviceStorageFile> > &
 
   while (NS_SUCCEEDED(files->GetNextFile(getter_AddRefs(f))) && f) {
 
-    int64_t msecs;
+    PRTime msecs;
     f->GetLastModifiedTime(&msecs);
 
     if (msecs < aSince) {
diff --git a/dom/plugins/base/nsPluginHost.cpp b/dom/plugins/base/nsPluginHost.cpp
index 49caa409e3c..b4233fab780 100644
--- a/dom/plugins/base/nsPluginHost.cpp
+++ b/dom/plugins/base/nsPluginHost.cpp
@@ -2004,7 +2004,7 @@ namespace {
 
 int64_t GetPluginLastModifiedTime(const nsCOMPtr<nsIFile>& localfile)
 {
-  int64_t fileModTime = LL_ZERO;
+  PRTime fileModTime = LL_ZERO;
 
 #if defined(XP_MACOSX)
   // On OS X the date of a bundle's "contents" (i.e. of its Info.plist file)
diff --git a/image/src/imgLoader.cpp b/image/src/imgLoader.cpp
index f51a666f040..ea51e8def3c 100644
--- a/image/src/imgLoader.cpp
+++ b/image/src/imgLoader.cpp
@@ -1284,7 +1284,7 @@ bool imgLoader::ValidateEntry(imgCacheEntry *aEntry,
     nsCOMPtr<nsIFile> theFile;
     rv = fileUrl->GetFile(getter_AddRefs(theFile));
     if (NS_SUCCEEDED(rv)) {
-      int64_t fileLastMod;
+      PRTime fileLastMod;
       rv = theFile->GetLastModifiedTime(&fileLastMod);
       if (NS_SUCCEEDED(rv)) {
         // nsIFile uses millisec, NSPR usec
diff --git a/modules/libjar/zipwriter/src/nsZipWriter.cpp b/modules/libjar/zipwriter/src/nsZipWriter.cpp
index 35594ce0cce..26d946d9d3e 100644
--- a/modules/libjar/zipwriter/src/nsZipWriter.cpp
+++ b/modules/libjar/zipwriter/src/nsZipWriter.cpp
@@ -364,7 +364,7 @@ NS_IMETHODIMP nsZipWriter::AddEntryFile(const nsACString & aZipEntry,
     rv = aFile->IsDirectory(&isdir);
     NS_ENSURE_SUCCESS(rv, rv);
 
-    int64_t modtime;
+    PRTime modtime;
     rv = aFile->GetLastModifiedTime(&modtime);
     NS_ENSURE_SUCCESS(rv, rv);
     modtime *= PR_USEC_PER_MSEC;
diff --git a/netwerk/base/src/nsDirectoryIndexStream.cpp b/netwerk/base/src/nsDirectoryIndexStream.cpp
index b7fb7ed6396..53e690afaa7 100644
--- a/netwerk/base/src/nsDirectoryIndexStream.cpp
+++ b/netwerk/base/src/nsDirectoryIndexStream.cpp
@@ -278,7 +278,7 @@ nsDirectoryIndexStream::Read(char* aBuf, uint32_t aCount, uint32_t* aReadCount)
             int64_t fileSize = 0;
             current->GetFileSize( &fileSize );
 
-            int64_t fileInfoModifyTime = 0;
+            PRTime fileInfoModifyTime = 0;
             current->GetLastModifiedTime( &fileInfoModifyTime );
             fileInfoModifyTime *= PR_USEC_PER_MSEC;
 
diff --git a/profile/dirserviceprovider/src/nsProfileLock.cpp b/profile/dirserviceprovider/src/nsProfileLock.cpp
index 3f38bc43f7a..b5db8a1ad01 100644
--- a/profile/dirserviceprovider/src/nsProfileLock.cpp
+++ b/profile/dirserviceprovider/src/nsProfileLock.cpp
@@ -426,7 +426,7 @@ PR_BEGIN_MACRO                                                          \
 }
 #endif /* XP_UNIX */
 
-nsresult nsProfileLock::GetReplacedLockTime(int64_t *aResult) {
+nsresult nsProfileLock::GetReplacedLockTime(PRTime *aResult) {
     *aResult = mReplacedLockTime;
     return NS_OK;
 }
diff --git a/profile/dirserviceprovider/src/nsProfileLock.h b/profile/dirserviceprovider/src/nsProfileLock.h
index ad66a7f5e52..a51e25e145c 100644
--- a/profile/dirserviceprovider/src/nsProfileLock.h
+++ b/profile/dirserviceprovider/src/nsProfileLock.h
@@ -59,11 +59,11 @@ public:
     /**
      * Get the modification time of a replaced profile lock, otherwise 0.
      */
-    nsresult                GetReplacedLockTime(int64_t* aResult);
+    nsresult                GetReplacedLockTime(PRTime* aResult);
 
 private:
     bool                    mHaveLock;
-    int64_t                 mReplacedLockTime;
+    PRTime                  mReplacedLockTime;
 
 #if defined (XP_WIN)
     HANDLE                  mLockFileHandle;
diff --git a/rdf/datasource/src/nsFileSystemDataSource.cpp b/rdf/datasource/src/nsFileSystemDataSource.cpp
index 40aebb60b68..e9b4ed2c400 100644
--- a/rdf/datasource/src/nsFileSystemDataSource.cpp
+++ b/rdf/datasource/src/nsFileSystemDataSource.cpp
@@ -1133,7 +1133,7 @@ FileSystemDataSource::GetLastMod(nsIRDFResource *source, nsIRDFDate **aResult)
     // ensure that we DO NOT resolve aliases
     aFile->SetFollowLinks(false);
 
-    int64_t lastModDate;
+    PRTime lastModDate;
     if (NS_FAILED(rv = aFile->GetLastModifiedTime(&lastModDate)))
         return(rv);
 
diff --git a/toolkit/components/filepicker/nsFileView.cpp b/toolkit/components/filepicker/nsFileView.cpp
index 1e4f3e0d234..cda6e7181a9 100644
--- a/toolkit/components/filepicker/nsFileView.cpp
+++ b/toolkit/components/filepicker/nsFileView.cpp
@@ -750,7 +750,7 @@ nsFileView::GetCellText(int32_t aRow, nsITreeColumn* aCol,
   if (NS_LITERAL_STRING("FilenameColumn").Equals(colID)) {
     curFile->GetLeafName(aCellText);
   } else if (NS_LITERAL_STRING("LastModifiedColumn").Equals(colID)) {
-    int64_t lastModTime;
+    PRTime lastModTime;
     curFile->GetLastModifiedTime(&lastModTime);
     // XXX FormatPRTime could take an nsAString&
     nsAutoString temp;
@@ -946,7 +946,7 @@ SortDateCallback(const void* aElement1, const void* aElement2, void* aContext)
   nsIFile* file1 = *static_cast<nsIFile* const *>(aElement1);
   nsIFile* file2 = *static_cast<nsIFile* const *>(aElement2);
 
-  int64_t time1, time2;
+  PRTime time1, time2;
   file1->GetLastModifiedTime(&time1);
   file2->GetLastModifiedTime(&time2);
 
diff --git a/toolkit/components/places/Database.cpp b/toolkit/components/places/Database.cpp
index e2979d879ce..0f65472d7b5 100644
--- a/toolkit/components/places/Database.cpp
+++ b/toolkit/components/places/Database.cpp
@@ -90,7 +90,7 @@ hasRecentCorruptDB()
     if (NS_SUCCEEDED(currFile->GetLeafName(leafName)) &&
         leafName.Length() >= DATABASE_CORRUPT_FILENAME.Length() &&
         leafName.Find(".corrupt", DATABASE_FILENAME.Length()) != -1) {
-      int64_t lastMod = 0;
+      PRTime lastMod = 0;
       currFile->GetLastModifiedTime(&lastMod);
       NS_ENSURE_TRUE(lastMod > 0, false);
       return (PR_Now() - lastMod) > RECENT_BACKUP_TIME_MICROSEC;
diff --git a/toolkit/components/startup/nsAppStartup.cpp b/toolkit/components/startup/nsAppStartup.cpp
index 14c806f952f..057f688f8e8 100644
--- a/toolkit/components/startup/nsAppStartup.cpp
+++ b/toolkit/components/startup/nsAppStartup.cpp
@@ -957,7 +957,7 @@ nsAppStartup::TrackStartupCrashBegin(bool *aIsSafeModeNecessary)
 
   xr->GetInSafeMode(&inSafeMode);
 
-  int64_t replacedLockTime;
+  PRTime replacedLockTime;
   rv = xr->GetReplacedLockTime(&replacedLockTime);
 
   if (NS_FAILED(rv) || !replacedLockTime) {
diff --git a/toolkit/profile/nsIToolkitProfile.idl b/toolkit/profile/nsIToolkitProfile.idl
index 084258c1106..2e217bb96b0 100644
--- a/toolkit/profile/nsIToolkitProfile.idl
+++ b/toolkit/profile/nsIToolkitProfile.idl
@@ -34,7 +34,7 @@ interface nsIProfileLock : nsISupports
     /**
      * The timestamp of an existing profile lock at lock time.
      */
-    readonly attribute int64_t replacedLockTime;
+    readonly attribute PRTime replacedLockTime;
 
     /**
      * Unlock the profile.
diff --git a/toolkit/profile/nsToolkitProfileService.cpp b/toolkit/profile/nsToolkitProfileService.cpp
index 150f690fa86..8add04c79f4 100644
--- a/toolkit/profile/nsToolkitProfileService.cpp
+++ b/toolkit/profile/nsToolkitProfileService.cpp
@@ -352,7 +352,7 @@ nsToolkitProfileLock::Unlock()
 }
 
 NS_IMETHODIMP
-nsToolkitProfileLock::GetReplacedLockTime(int64_t *aResult)
+nsToolkitProfileLock::GetReplacedLockTime(PRTime *aResult)
 {
     mLock.GetReplacedLockTime(aResult);
     return NS_OK;
diff --git a/toolkit/xre/nsAppRunner.cpp b/toolkit/xre/nsAppRunner.cpp
index 17e6478cabc..4cb024906ae 100644
--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -810,7 +810,7 @@ nsXULAppInfo::InvalidateCachesOnRestart()
 }
 
 NS_IMETHODIMP
-nsXULAppInfo::GetReplacedLockTime(int64_t *aReplacedLockTime)
+nsXULAppInfo::GetReplacedLockTime(PRTime *aReplacedLockTime)
 {
   if (!gProfileLock)
     return NS_ERROR_NOT_AVAILABLE;
diff --git a/xpcom/io/nsIFile.idl b/xpcom/io/nsIFile.idl
index 9433c132f60..a9b5cb7c085 100644
--- a/xpcom/io/nsIFile.idl
+++ b/xpcom/io/nsIFile.idl
@@ -188,8 +188,8 @@ interface nsIFile : nsISupports
      *  midnight (00:00:00), January 1, 1970 Greenwich Mean
      *  Time (GMT).
      */
-    attribute int64_t lastModifiedTime;
-    attribute int64_t lastModifiedTimeOfLink;
+    attribute PRTime lastModifiedTime;
+    attribute PRTime lastModifiedTimeOfLink;
 
     /**
      *  WARNING!  On the Mac, getting/setting the file size with nsIFile
diff --git a/xpcom/io/nsLocalFileOS2.cpp b/xpcom/io/nsLocalFileOS2.cpp
index 0bed86dec1f..83becde55f9 100644
--- a/xpcom/io/nsLocalFileOS2.cpp
+++ b/xpcom/io/nsLocalFileOS2.cpp
@@ -1702,7 +1702,7 @@ nsLocalFile::Remove(bool recursive)
 }
 
 NS_IMETHODIMP
-nsLocalFile::GetLastModifiedTime(int64_t *aLastModifiedTime)
+nsLocalFile::GetLastModifiedTime(PRTime *aLastModifiedTime)
 {
     // Check we are correctly initialized.
     CHECK_mWorkingPath();
@@ -1723,14 +1723,14 @@ nsLocalFile::GetLastModifiedTime(int64_t *aLastModifiedTime)
 
 
 NS_IMETHODIMP
-nsLocalFile::GetLastModifiedTimeOfLink(int64_t *aLastModifiedTime)
+nsLocalFile::GetLastModifiedTimeOfLink(PRTime *aLastModifiedTime)
 {
     return NS_ERROR_NOT_IMPLEMENTED;
 }
 
 
 NS_IMETHODIMP
-nsLocalFile::SetLastModifiedTime(int64_t aLastModifiedTime)
+nsLocalFile::SetLastModifiedTime(PRTime aLastModifiedTime)
 {
     // Check we are correctly initialized.
     CHECK_mWorkingPath();
@@ -1740,13 +1740,13 @@ nsLocalFile::SetLastModifiedTime(int64_t aLastModifiedTime)
 
 
 NS_IMETHODIMP
-nsLocalFile::SetLastModifiedTimeOfLink(int64_t aLastModifiedTime)
+nsLocalFile::SetLastModifiedTimeOfLink(PRTime aLastModifiedTime)
 {
     return NS_ERROR_NOT_IMPLEMENTED;
 }
 
 nsresult
-nsLocalFile::SetModDate(int64_t aLastModifiedTime)
+nsLocalFile::SetModDate(PRTime aLastModifiedTime)
 {
     nsresult rv = Stat();
 
diff --git a/xpcom/io/nsLocalFileUnix.cpp b/xpcom/io/nsLocalFileUnix.cpp
index 5f30160a093..aebadcacbc8 100644
--- a/xpcom/io/nsLocalFileUnix.cpp
+++ b/xpcom/io/nsLocalFileUnix.cpp
@@ -963,7 +963,7 @@ nsLocalFile::Remove(bool recursive)
 }
 
 NS_IMETHODIMP
-nsLocalFile::GetLastModifiedTime(int64_t *aLastModTime)
+nsLocalFile::GetLastModifiedTime(PRTime *aLastModTime)
 {
     CHECK_mPath();
     NS_ENSURE_ARG(aLastModTime);
@@ -971,17 +971,17 @@ nsLocalFile::GetLastModifiedTime(int64_t *aLastModTime)
     PRFileInfo64 info;
     if (PR_GetFileInfo64(mPath.get(), &info) != PR_SUCCESS)
         return NSRESULT_FOR_ERRNO();
-    int64_t modTime = int64_t(info.modifyTime);
+    PRTime modTime = info.modifyTime;
     if (modTime == 0)
         *aLastModTime = 0;
     else
-        *aLastModTime = modTime / int64_t(PR_USEC_PER_MSEC);
+        *aLastModTime = modTime / PR_USEC_PER_MSEC;
 
     return NS_OK;
 }
 
 NS_IMETHODIMP
-nsLocalFile::SetLastModifiedTime(int64_t aLastModTime)
+nsLocalFile::SetLastModifiedTime(PRTime aLastModTime)
 {
     CHECK_mPath();
 
@@ -992,7 +992,7 @@ nsLocalFile::SetLastModifiedTime(int64_t aLastModTime)
         ut.actime = mCachedStat.st_atime;
 
         // convert milliseconds to seconds since the unix epoch
-        ut.modtime = (time_t)(double(aLastModTime) / PR_MSEC_PER_SEC);
+        ut.modtime = (time_t)(aLastModTime / PR_MSEC_PER_SEC);
         result = utime(mPath.get(), &ut);
     } else {
         result = utime(mPath.get(), nullptr);
@@ -1001,7 +1001,7 @@ nsLocalFile::SetLastModifiedTime(int64_t aLastModTime)
 }
 
 NS_IMETHODIMP
-nsLocalFile::GetLastModifiedTimeOfLink(int64_t *aLastModTimeOfLink)
+nsLocalFile::GetLastModifiedTimeOfLink(PRTime *aLastModTimeOfLink)
 {
     CHECK_mPath();
     NS_ENSURE_ARG(aLastModTimeOfLink);
@@ -1009,7 +1009,7 @@ nsLocalFile::GetLastModifiedTimeOfLink(int64_t *aLastModTimeOfLink)
     struct STAT sbuf;
     if (LSTAT(mPath.get(), &sbuf) == -1)
         return NSRESULT_FOR_ERRNO();
-    *aLastModTimeOfLink = int64_t(sbuf.st_mtime) * int64_t(PR_MSEC_PER_SEC);
+    *aLastModTimeOfLink = PRTime(sbuf.st_mtime) * PR_MSEC_PER_SEC;
 
     return NS_OK;
 }
@@ -1018,7 +1018,7 @@ nsLocalFile::GetLastModifiedTimeOfLink(int64_t *aLastModTimeOfLink)
  * utime(2) may or may not dereference symlinks, joy.
  */
 NS_IMETHODIMP
-nsLocalFile::SetLastModifiedTimeOfLink(int64_t aLastModTimeOfLink)
+nsLocalFile::SetLastModifiedTimeOfLink(PRTime aLastModTimeOfLink)
 {
     return SetLastModifiedTime(aLastModTimeOfLink);
 }
diff --git a/xpcom/io/nsLocalFileWin.cpp b/xpcom/io/nsLocalFileWin.cpp
index d62d928c797..6a10056f5e8 100644
--- a/xpcom/io/nsLocalFileWin.cpp
+++ b/xpcom/io/nsLocalFileWin.cpp
@@ -2250,7 +2250,7 @@ nsLocalFile::Remove(bool recursive)
 }
 
 NS_IMETHODIMP
-nsLocalFile::GetLastModifiedTime(int64_t *aLastModifiedTime)
+nsLocalFile::GetLastModifiedTime(PRTime *aLastModifiedTime)
 {
     // Check we are correctly initialized.
     CHECK_mWorkingPath();
@@ -2275,7 +2275,7 @@ nsLocalFile::GetLastModifiedTime(int64_t *aLastModifiedTime)
 
 
 NS_IMETHODIMP
-nsLocalFile::GetLastModifiedTimeOfLink(int64_t *aLastModifiedTime)
+nsLocalFile::GetLastModifiedTimeOfLink(PRTime *aLastModifiedTime)
 {
     // Check we are correctly initialized.
     CHECK_mWorkingPath();
@@ -2299,7 +2299,7 @@ nsLocalFile::GetLastModifiedTimeOfLink(int64_t *aLastModifiedTime)
 
 
 NS_IMETHODIMP
-nsLocalFile::SetLastModifiedTime(int64_t aLastModifiedTime)
+nsLocalFile::SetLastModifiedTime(PRTime aLastModifiedTime)
 {
     // Check we are correctly initialized.
     CHECK_mWorkingPath();
@@ -2322,7 +2322,7 @@ nsLocalFile::SetLastModifiedTime(int64_t aLastModifiedTime)
 
 
 NS_IMETHODIMP
-nsLocalFile::SetLastModifiedTimeOfLink(int64_t aLastModifiedTime)
+nsLocalFile::SetLastModifiedTimeOfLink(PRTime aLastModifiedTime)
 {
     // The caller is assumed to have already called IsSymlink 
     // and to have found that this file is a link. 
@@ -2335,7 +2335,7 @@ nsLocalFile::SetLastModifiedTimeOfLink(int64_t aLastModifiedTime)
 }
 
 nsresult
-nsLocalFile::SetModDate(int64_t aLastModifiedTime, const PRUnichar *filePath)
+nsLocalFile::SetModDate(PRTime aLastModifiedTime, const PRUnichar *filePath)
 {
     // The FILE_FLAG_BACKUP_SEMANTICS is required in order to change the
     // modification time for directories.
diff --git a/xpcom/system/nsIXULRuntime.idl b/xpcom/system/nsIXULRuntime.idl
index 4d512041dc3..07466fc070f 100644
--- a/xpcom/system/nsIXULRuntime.idl
+++ b/xpcom/system/nsIXULRuntime.idl
@@ -88,7 +88,7 @@ interface nsIXULRuntime : nsISupports
    * this startup. Used to know the last time the profile was used and not
    * closed cleanly. This is set to 0 if there was no existing profile lock.
    */
-  readonly attribute int64_t replacedLockTime;
+  readonly attribute PRTime replacedLockTime;
 
   /**
    * Local ID of the minidump generated when the process crashed