diff --git a/dom/file/BaseBlobImpl.cpp b/dom/file/BaseBlobImpl.cpp
index 2db3145c5fd5..c18916335db1 100644
--- a/dom/file/BaseBlobImpl.cpp
+++ b/dom/file/BaseBlobImpl.cpp
@@ -64,7 +64,8 @@ BaseBlobImpl::GetLastModified(ErrorResult& aRv)
 {
   MOZ_ASSERT(mIsFile, "Should only be called on files");
   if (IsDateUnknown()) {
-    mLastModificationDate = nsRFPService::ReduceTimePrecisionAsUSecs(PR_Now());
+    mLastModificationDate = nsRFPService::ReduceTimePrecisionAsUSecs(PR_Now(), 0);
+    // mLastModificationDate is an absolute timestamp so we supply a zero context mix-in
   }
 
   return mLastModificationDate / PR_USEC_PER_MSEC;
diff --git a/dom/file/MultipartBlobImpl.cpp b/dom/file/MultipartBlobImpl.cpp
index 33cfe6fe2b1f..7e4e1336b5a1 100644
--- a/dom/file/MultipartBlobImpl.cpp
+++ b/dom/file/MultipartBlobImpl.cpp
@@ -269,7 +269,8 @@ MultipartBlobImpl::SetLengthAndModifiedDate(ErrorResult& aRv)
     //   x.getTime() < f.dateModified.getTime()
     // could fail.
     mLastModificationDate = nsRFPService::ReduceTimePrecisionAsUSecs(
-      lastModifiedSet ? lastModified * PR_USEC_PER_MSEC : JS_Now());
+      lastModifiedSet ? lastModified * PR_USEC_PER_MSEC : JS_Now(), 0);
+    // mLastModificationDate is an absolute timestamp so we supply a zero context mix-in
   }
 }
 
diff --git a/toolkit/components/resistfingerprinting/nsRFPService.cpp b/toolkit/components/resistfingerprinting/nsRFPService.cpp
index 8d6963bad384..33bfbbb168e6 100755
--- a/toolkit/components/resistfingerprinting/nsRFPService.cpp
+++ b/toolkit/components/resistfingerprinting/nsRFPService.cpp
@@ -557,7 +557,7 @@ nsRFPService::ReduceTimePrecisionAsUSecsWrapper(double aTime)
     aTime,
     MicroSeconds,
     TimerResolution(),
-    0,
+    0, /* For absolute timestamps (all the JS engine does), supply zero context mixin */
     TimerPrecisionType::All);
 }