Bug 1556935 - add identity.fxaccounts.enabled to about:support whitelist r=jaws

Differential Revision: https://phabricator.services.mozilla.com/D34736

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

toolkit/modules/Troubleshoot.jsm

@@ -56,6 +56,7 @@ const PREFS_WHITELIST = [
   "general.useragent.",
   "gfx.",
   "html5.",
+  "identity.fxaccounts.enabled",
   "idle.",
   "image.",
   "javascript.",