STR: - install Fx nightly (OSX for me) - install containers testpilot addon https://testpilot.firefox.com/experiments/containers - add containers icon (4 squares in a square, except the top right square is a `+`) to nav bar - restart Fx nightly for an update Expected result: - containers icon is in nav bar Actual result: - containers icon is missing. Upon a quit and reopen, the containers icon reappears. Per https://bugzilla.mozilla.org/show_bug.cgi?id=1385630#c66 , the output of CustomizableUI.getWidgetIdsInArea("nav-bar"); is: Array [ "customizableui-special-spring144", "back-button", "forward-button", "stop-reload-button", "urlbar-container", "downloads-button", "new-tab-button", "_testpilot-containers-browser-action", "pocket-button", "jid1-mnnxcxisbpnsxq_jetpack-browser…", 7 more… ] 7 more includes "action-button--testpilot-addon-main" "_cd7e22de-2e34-40f0-aeff-cec824cbccac_-browser-action" "snoozetabs_mozilla_com-browser-action" "_forest-firefox-addon-browser-action" "screenshots_mozilla_org-browser-action" "library-button" "geckoprofiler_mozilla_com-browser-action"

Thanks so much for the prompt response and bug filing. Good news: I'm 99% sure this will be fixed by bug 1399517. I think it's because of the old "pocket-button" placement that's still in your navbar. TBH, I'm a bit surprised *only* the containers item would disappear and not the other items that occur after the containers item... but anyway. Let's wait until 1399517 lands. I'll track this so I remember to doublecheck with you that the issue is fixed after that lands.

Hey Aki, this should be fixed on yesterday's "late" nightly (buildid 20170919220202), or today's nightly if that's simpler. Can you confirm that it's fixed for you, too?

Yes! I have the containers icon on update-restart. Thank you!

Thanks Gijs, I think there was a another filed on behalf of Aki for this exact bug. I will chase it down. Thanks both.