Panel does not open after update to Firefox 64

[shankargopal]

• Is "Firefox will: Never remember history" in the Firefox Preferences/Options under "Privacy & Security > History" selected? Yes/No: No
• Are you using Firefox in a Private Window? Yes/No: No
• Can you see a grayed out but ticked Checkbox with the description "Enable Container Tabs" in the Firefox Preferences/Options under "Tabs"? Yes/No: Yes
• Multi-Account Containers Version: 6.0.1
• Operating System + Version: Debian Linux Testing, kernel 4.15.0-2-686-pae
• Firefox Version: 64.0
• Other installed Add-ons + Version + Enabled/Disabled-Status:

Name Version Enabled
Cookie AutoDelete 2.2.0 true
Firefox Multi-Account Containers 6.0.1 true
Link Cleaner 1.5 true
Privacy Badger 2018.12.17 true
Textarea Cache 4.0.1 true
Tridactyl 1.14.6 true
uBlock Origin 1.17.4 true
User-Agent Switcher 0.2.4 true
Video DownloadHelper 7.3.5 true
Bloody Vikings! 0.9.4 false
Decentraleyes 2.0.8 false
Temporary Containers 0.90 true

Actual behavior

When I click on the icon for MAC, I get a small empty box instead of the list of containers. I'm attaching a screenshot. The full list of containers is still visible in the Preferences.

Expected behavior

The normal list of containers.

Steps to reproduce

1. Click on icon
2. Panel does not open

Notes

As far as I can tell, this problem started after I updated Firefox to 64.0.

The Cookie AutoDelete panel also appears to have stopped working at the same time??

[shankargopal]

It seems to be completely erratic. I restarted Firefox several times before posting the above bug - it made no difference. Some time later, I re-enabled Temporary Containers, and that also made no difference (including after a restart). But then after some time I restarted Firefox after closing it for some other work, and MAC started working normally again.

This pattern - not working for some time, then working again - repeated itself again today.

[mcepl]

For me it was after upgrade to FF 66.*, but the results looks the same.

[stoically]

This also happens for me with other Add-on popups, so it seems that it's not MAC specific.

[dannycolin]

Closing since it was a bug in Firefox itself that should be fixed by now. If you still experience it, please file a bug report directly on bugzilla.mozilla.org.