This is already handled by Firefox's very own Multi-Account Containers extension.
I like to add Sticky Window Containers for extra functionality. Sidebery also works well with containers.
This is my choice as well. Sadly it has long since stopped getting updates - while basic RSS features will always work, hoping Feedly integration keeps working.
This grinds my gears everytime questions of this form show up: X people of Reddit, what is the most FUCKED UP Y you have seen while Z?
It doesn't help that we have pinned posts from many communities hogging the top space in many sorting options, without a way to get rid of them.
Apart from the ones already mentioned,
- being able to collapse all threads in a post to only show parent-level comments
- keyboard shortcuts ala RES (esp the J-K navigation)
- more themes (the default ones suck)
- more image improvements
The devs were hoping that they can keep their apps up and their livelihoods without too much additional work, that's fair from them I suppose. But they should definitely be taking a hard look at porting their existing apps for the Fediverse, if they aren't yet.