diff --git a/xpcom/base/FunctionTimer.cpp b/xpcom/base/FunctionTimer.cpp
index 5b994fe68f9..0d25eb414a6 100644
--- a/xpcom/base/FunctionTimer.cpp
+++ b/xpcom/base/FunctionTimer.cpp
@@ -86,6 +86,7 @@ FunctionTimer::InitTimers()
 }
 
 FunctionTimerLog::FunctionTimerLog(const char *fname)
+    : mLatest(sAppStart)
 {
     if (strcmp(fname, "stdout") == 0) {
         mFile = stdout;
@@ -119,11 +120,18 @@ void
 FunctionTimerLog::LogString(const char *str)
 {
     if (mFile) {
-        TimeDuration elapsed = TimeStamp::Now() - sAppStart;
+        mLatest = TimeStamp::Now();
+        TimeDuration elapsed = mLatest - sAppStart;
         fprintf((FILE*)mFile, "[% 9.2f] %s\n", elapsed.ToSeconds() * 1000.0, str);
     }
 }
 
+TimeDuration
+FunctionTimerLog::LatestSinceStartup() const
+{
+    return mLatest - sAppStart;
+}
+
 int
 FunctionTimer::ft_vsnprintf(char *str, int maxlen, const char *fmt, va_list args)
 {
diff --git a/xpcom/base/FunctionTimer.h b/xpcom/base/FunctionTimer.h
index 2362d2e7231..0d71ff25c0b 100644
--- a/xpcom/base/FunctionTimer.h
+++ b/xpcom/base/FunctionTimer.h
@@ -112,6 +112,11 @@
 #define NS_TIME_FUNCTION_ELAPSED_SINCE_MARK                             \
     ft__autogen.ElapsedSinceMark
 
+// A TimeDuration value representing the elapsed time between the
+// last logged event of any sort and the app startup.
+#define NS_TIME_FUNCTION_LATEST \
+    mozilla::FunctionTimer::LatestSinceStartup()
+
 #else
 
 #define NS_TIME_FUNCTION do { } while (0)
@@ -122,6 +127,7 @@
 #define NS_TIME_FUNCTION_MARK(...) do { } while (0)
 #define NS_TIME_FUNCTION_ELAPSED (0)
 #define NS_TIME_FUNCTION_ELAPSED_SINCE_MARK (0)
+#define NS_TIME_FUNCTION_LATEST (mozilla::TimeDuration(0))
 
 #endif
 
@@ -135,8 +141,11 @@ public:
 
     void LogString(const char *str);
 
+    TimeDuration LatestSinceStartup() const;
+
 private:
     void *mFile;
+    TimeStamp mLatest;
 };
 
 class NS_COM FunctionTimer
@@ -199,6 +208,10 @@ public:
         return 0.0;
     }
 
+    static inline TimeDuration LatestSinceStartup() {
+        return sLog ? sLog->LatestSinceStartup() : TimeDuration(0);
+    }
+
     FunctionTimer(double minms, const char *s, ...)
         : mMinMs(minms), mHasMinMs(PR_TRUE),
           mEnabled(sLog && s && *s), mDepth(++sDepth)