This issue is stale because it has been open for 30 days with no activity.

Does it still happen?

yup still happen, same with Floorp and Librewolf as well

It still occurs on Zen, but works normal for me on Librewolf

yup still happen, same with Floorp and Librewolf as well

it's probably the extension's fault then, no?

yup still happen, same with Floorp and Librewolf as well

it's probably the extension's fault then, no?

@mauro-balades
It is working on Librewolf

I think I found a solution. Inspecting the Temporary Containers, you will immediately notice a lot of uncaught errors from showOrHide caused by L4943. The extension is trying to get a container with id firefox-default, but that does not exist.

Examining Temporary Containers source code, showOrHide is found in pageaction.ts with the line causing the throw at L43. For why it's throwing, in Firefox you never reach the else instead the if else on L31 is executed. In Zen that if else doesn't execute because the extension checks whether the default cookiestore id is being used by getting the browsers name which gives zen and appending -default, but the default cookiestore id is firefox-default. The else if doesn't execute as zen-default does not equal firefox-default and instead the else executes which causes the error.

Setting global.DEFAULT_STORE in /toolkit/components/extensions/parent/ext-toolkit.js to zen-default makes Automatic Mode in Temporary Containers functional.

I can't comment whether this fix breaks other container extensions. If they hardcoded checking cookieStoreId against firefox-default, then this fix would break them.