diff -up firefox-55.0/browser/app/profile/firefox.js.addons firefox-55.0/browser/app/profile/firefox.js
--- firefox-55.0/browser/app/profile/firefox.js.addons	2017-08-02 10:58:30.566363833 +0200
+++ firefox-55.0/browser/app/profile/firefox.js	2017-08-02 10:59:15.377216959 +0200
@@ -65,7 +65,8 @@ pref("extensions.systemAddon.update.url"
 
 // Disable add-ons that are not installed by the user in all scopes by default.
 // See the SCOPE constants in AddonManager.jsm for values to use here.
-pref("extensions.autoDisableScopes", 15);
+pref("extensions.autoDisableScopes", 0);
+pref("extensions.showMismatchUI", false);
 // Scopes to scan for changes at startup.
 pref("extensions.startupScanScopes", 0);
 
