Bug 1201374 - Add a telemetry probe to track how often F11 fullscreen mode is used (browser-fullscreen). r=ttaubert p=ally

browser/base/content/browser-fullScreen.js

@@ -95,6 +95,11 @@ var FullScreen = {
       // TabsInTitlebar._update() and bug 1173768.
       TabsInTitlebar.updateAppearance(true);
     }
+
+    if (enterFS) {
+      Services.telemetry.getHistogramById("FX_BROWSER_FULLSCREEN_USED")
+                        .add(1);
+    }
   },
 
   exitDomFullScreen : function() {

toolkit/components/telemetry/Histograms.json

@@ -4062,6 +4062,11 @@
     "extended_statistics_ok": true,
     "description": "Firefox: Time to initialize the bookmarks toolbar view (ms)"
   },
+  "FX_BROWSER_FULLSCREEN_USED": {
+    "expires_in_version": "46",
+    "kind": "count",
+    "description": "The number of times that a session enters browser fullscreen (f11-fullscreen)"
+  },
   "FX_NEW_WINDOW_MS": {
     "expires_in_version": "default",
     "kind": "exponential",