Containers with Transitions: Firefox add-on to pick container based on origin

Submission statement: this is a Firefox extension I've been working on for a while, forked from Multi-Account Containers (which unfortunately seems to be very lightly maintained/not seeing much further development). Apart from some papercut solutions (based on personal opinions: the close-and-reopen mechanism to pick the right container for a tab seems to cause TST physical pain, so I tried to reduce the cases where it fires), it adds one big feature, which is container transition rules: rather than just setting a single default container for a website, you can say that you want to open it in a particular container X whenever it was opened (via a link, redirect, ...) from container Y.

This solves a common issue I was encountering when browsing, where I'd start out with some Facebook tab (dutifully containerised), click some links in the chat, follow some more links from the pages arrived at, and before long I'd have a subtree of 30+ tabs all being in the Facebook container while having absolutely no business seeing my Facebook cookies.

There's more documentation and some usage examples on the addon page. Of course, this is beta-quality software. I'd appreciate if you could try it out and give feedback and bug reports. Also, you should disable Multi-Account Containers before running this, since they both hook into the same events and I don't want to know what happens if they disagree over what container a page should go into.

See also the Reddit discussion, where I provide some more rationale: https://old.reddit.com/r/firefox/comments/abpssw/containers_...