alt+a shortcut stopped working

I've been using alt+a to open new tabs in a multi account container for a long time. Recently that shortcut stopped working possibly with the update to v148 as indicated in this [https://www.reddit.com/r/firefox/comments/1rgymyt/as_of_v148_alta_hotkey_stopped_working_for_some/ reddit] thread. alt+a is not listed as a shortcut in about:keyboard or in about:addons > manage extension shortcuts or in my ubuntu shortcuts nor in any software I can think of thats running. I've disabled all add-ons except multi account containers and it still does not work. Changing the shortcut to another works fine. Why would just that shortcut stop working? What else can I do to diagnose the problem?