Bug 1501543 - Misleading message when DisableAppUpdate is true but the system administrator updates Firefox in place r=spohl,flod

Changed text
From: We have just installed an update in the background.
To: Firefox has just been updated in the background.

Differential Revision: https://phabricator.services.mozilla.com/D21019

--HG--
extra : moz-landing-system : lando

browser/base/content/aboutRestartRequired.xhtml

@@ -26,7 +26,7 @@
         </div>
         <div id="errorLongContent">
           <div id="errorLongDesc">
-            <p data-l10n-id="restart-required-intro"></p>
+            <p data-l10n-id="restart-required-intro-brand"></p>
             <p data-l10n-id="restart-required-description"></p>
           </div>
         </div>

browser/locales/en-US/browser/aboutRestartRequired.ftl

@@ -4,7 +4,7 @@
 
 restart-required-title = Restart Required
 restart-required-header = Sorry. We just need to do one small thing to keep going.
-restart-required-intro = We have just installed an update in the background. Click Restart { -brand-short-name } to finish
+restart-required-intro-brand = { -brand-short-name } has just been updated in the background. Click Restart { -brand-short-name } to finish
     applying it.
 restart-required-description = We will restore all your pages, windows and tabs afterwards, so you can be on your way quickly.