Issue 5660 - Check for runtime.getBrowserInfo API support

templates/geckoInfo.js.tmpl

 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 "use strict";
 
 exports.addonName = {{ basename|json }};
 exports.addonVersion = {{ version|json }};
 
 exports.application = "unknown";
 exports.applicationVersion = "0";
 
 exports.platform = "gecko";
 exports.platformVersion = "0";
 
 let match = /\brv:(\d+(?:\.\d+)?)\b/.exec(navigator.userAgent);
 if (match)
   exports.platformVersion = match[1];
 
-browser.runtime.getBrowserInfo().then(browserInfo =>
+// Firefox 50 does not support runtime.getBrowserInfo
+if ("getBrowserInfo" in browser.runtime)
 {
-  exports.application = browserInfo.name.toLowerCase();
-  exports.applicationVersion = browserInfo.version;
-});
+  browser.runtime.getBrowserInfo().then(browserInfo =>
+  {
+    exports.application = browserInfo.name.toLowerCase();
+    exports.applicationVersion = browserInfo.version;
+  });
+}
+else
+{
+  let browserInfo = /\bFirefox\/(\S+)/.exec(navigator.userAgent);
+  exports.application = "firefox";
+  if (browserInfo)
+    exports.applicationVersion = browserInfo[1];
+}