Could you clarify "recently" a bit more? Clearly it's after the release of uBlock Origin, but I'm pretty sure that there was a big effort to clean up memory use a few years ago.
Maybe it's poor Linux support, I have a distressingly high 4 digit number of tabs open on a Windows box and I don't think I've seen it go past 8gb with multiple weeks of runtime.
What do you with a 4 digit number of tabs? How can you even find what you are looking for? (Honest question, no attack)
I hardly ever have more than 10 tabs open, and aggressively close everything I am not working with. I also shut down my browser twice a day (2 working locations) and never restore the previous session. I do bookmark some pages, but as a matter of fact I notice that I hardly ever refer to my bookmarks. I don't have the feeling that I am missing out on anything.
Fail to go back and clear them out, mostly. Most were left open because of something relevant at the time, so I mostly need to spend a little time going through and nuking or nothing. There's been little friction due to leaving them open so it hasn't been a priority.
Pretty much the same thing that leaves some people with tens of thousands of messages in their inboxes (I deal with someone who does that and it makes my teeth itch, so my inbox isn't so bad).
Right, my private Gmail inbox has more than 70,000 conversations (no clue how many messages). Using search I typically find quickly what I want.
As a programmer who has spent significant time with performance work, having useless tabs in a browser would hurt me. But that Google has to search through a bit longer list of messages I can accept as the typical wastefulness of computing these days. (I am old enough to have done time-sharing on 4 MB with 11 other students on their VT100)
Type '%' (no quotes) followed by parts of the URL or title or both in the URL bar. Searches only your open tabs. I can usually find exactly what I want quite quickly.
Sadly, the sites out there have changed far more than any of the browsers have, and not for the better. They load a ton of crap that does not contribute to the value delivered to the user, but instead contribute value to the site owner and the dozen layers of intermediaries in between user and site owner.
If you have a limited number of sites that blow FF memory usage up like that within a limited time (and that you're willing to share in a bug report) then that might be something helpful to report. Failing that, there may be some telemetry available that might be able to identify problem areas, though I'm not sure what details would be.
Maybe it's poor Linux support, I have a distressingly high 4 digit number of tabs open on a Windows box and I don't think I've seen it go past 8gb with multiple weeks of runtime.
Edit: Win10 Pro on a Xeon with 48gb ram available