Firefox containers vs profiles, how contained are they?

Firefox containers vs profiles, how contained are they?

As a "privacy by compartmentalization" measure I used to implement in my day to day surfing was to separate each part into Firefox profiles.
Work, Study, Finance...

Recently I learned about Firefox Containers.
It would be way more convenient to use everything in one profile separated by containers.

However my questions are:

1. How strong are these containers? Can a tab in one container in ANY WAY know about activity in other containers? or is that impossible by design?
2. I use some extensions like cookie auto-delete and Ublock Origin, Can these in any way leak data from one container to the other?

And the last thing, it really matters that no leaks happen, if it's 100% the same level of isolation as Firefox profiles please let me know.
And if you can add sources too it would be great.