Bug 1276027 - Add a Telemetry probe to track how often Firefox is used as the default handler. r=bsmedberg,rstrong

MozReview-Commit-ID: Ar3MaKeUIdz

--HG--
extra : rebase_source : 05c9003c9ae95ca304f233b34b08ef492c524360

browser/components/nsBrowserContentHandler.js

@@ -710,6 +710,18 @@ nsDefaultCommandLineHandler.prototype = {
 
   /* nsICommandLineHandler */
   handle : function dch_handle(cmdLine) {
+    // The -url flag is inserted by the operating system when the default
+    // application handler is used. We check for default browser to remove
+    // instances where users explicitly decide to "open with" the browser.
+    // Note that users who launch firefox manually with the -url flag will
+    // get erroneously counted.
+    if (cmdLine.findFlag("url", false) &&
+        ShellService.isDefaultBrowser(false, false)) {
+      try {
+        Services.telemetry.getHistogramById("FX_STARTUP_EXTERNAL_CONTENT_HANDLER").add();
+      } catch (e) {}
+    }
+
     var urilist = [];
 
     if (AppConstants.platform == "win") {

toolkit/components/telemetry/Histograms.json

@@ -4452,6 +4452,13 @@
     "releaseChannelCollection": "opt-out",
     "description": "The browser that was the default on the initial profile migration. The values correspond to the internal browser ID (see MigrationUtils.jsm)"
   },
+  "FX_STARTUP_EXTERNAL_CONTENT_HANDLER": {
+    "bug_numbers": [1276027],
+    "alert_emails": ["jaws@mozilla.com"],
+    "expires_in_version": "53",
+    "kind": "count",
+    "description": "Count how often the browser is opened as an external app handler. This is generally used when the browser is set as the default browser."
+  },
   "INPUT_EVENT_RESPONSE_MS": {
     "alert_emails": ["perf-telemetry-alerts@mozilla.com"],
     "bug_numbers": [1235908],