If I understand what you want correctly: the Firefox multi account container extension (is that the default one?) allows to "manage containers" and by clicking on the one you want you can select "limit to designated sites" so you can, from a container, click a non containerized link and get that link opened in the default/different container

Thank you thank you! That's fantastic! I wish I didn't have to manually assign containers but ya know what, good enough.

In temporary containers you can set up what should happen on different actions (left click, ctrl+click, etc) and different domains.

https://github.com/stoically/temporary-containers/wiki/Globa...

> If you want to isolate Facebook and click a link to Spotify it will open Spotify in the Facebook container :(

If you are talking about the Temporary containers extension, that's not the case. The extension is not the most easy to use, but it certainly supports opening Spotify in a different container when clicking a link in FB. You either don't have the Navigation→Target Domain set to Different from Tab Domain & Subdomains or you have Exclusion Patterns set which exempt Spotify.

Just enable "Default container" in its settings to isolate everything. (For advanced usage, also see the help button)

Right-click the link and click "Open in new container tab > " and click the container you want.