Have you tried to load FireFox in Private mode to see if it makes any differences.

If you mean the "Always use private browsing mode" in settings - I could try that, however, I'd like to know that my session would be saved(as I've had issues with that, and the only solution Firefox has is a "closed window" tab, if it's cached) and, I assume, this is a safe way to try firefox without cache and cookies? I apologize, it hasn't crossed my mind right away, and I'd like to point out that it "could" have something to do with youtube, because after 30-60 seconds if that slow loading(browser is responding, but the pages just aren't loading) - the first thing I see is youtube notifications if there are any.

Even if it's solved by some maintenance\radical measure like clearing cache and\or reinstalling, even with the bookmark import - I'd still like to know why is the loading speed so bottlenecked and if it is a random read issue or something else. Maybe there's some setting that should auto-clear cache or data from websites that are accessed less than once a month\season.

This is to find out what is causing the issue. You have to trouble shoot here if you want to narrow down what causing the problems. You can always redo your sessions later by pin to tab or making them bookmark to go to later.

Thanks for suggesting the private mode, it did help, and, as I said about caching - it did point me in the right direction. Turns out that Firefox DID try to pull cache history from... years back. Ironically, I've checked the use date, and there have been some sites I visited indeed like 1-2 weeks ago, which *weren't* pulled upon start-up, and hundreds of sites that I *do not* use on a daily basis if at all - were, for some reason, *all* pulled upon start-up. That confirms my guess about random read and explains why that was so.

What I still do not understand is why the hell was Firefox doing that? Was it to enable bookmarks? Because I'm pretty sure more than half of that cache wasn't bookmarked and is from any "places you only visit once" that "force you to consent cookies". I initially wanted to manually clear cache, because, like I said, I do not like radical solutions, but there was too much of it to sift through, so, yeah, total cache wipe did help, now the start-up isn't random read and is bulk loading. But the thing is - not *ALL* cache has been loaded. Like 10% was marked as used "last year" and even some "recent" websites haven't been loaded. Which is kind of counter-intuitive. As I said in my first reply - shouldn't there be some mechanism that straight-up archived cache from 1-3 months ago? Because it's almost like it works the OTHER way around. And I'd still like to know why that is, if this possible in this thread. I'll mark my post for solution, give you a thumbs-up, but it's a maintenance solution of a problem that most likely will appear again, or might happen to someone else. At the very least I'd like to know if it's back-end(and maybe Firefox would resolve it with its frequent updates) or front-end, and I either have some wrong settings or the extensions.

Speaking of extension, as I said - ublock origin and browsec vpn. Ublock has some extra filters for automatic cookie denial, I'm not even sure if they work, didn't check. And browsec isn't always on, let alone on at start-up. So could they be forcing the cache? With the cache gone - I can't quite test it now, maybe if I remember(or this issue returns and reminds me, heh) later I'll check the cache that is forced upon start-up, then delete\reinstall the extensions and see if anything changes.

But the bottom line is - if the cache was handled\archived by the browser, this wouldn't have happened. Sure, some 1.5gb of cache is bad, but old system are old systems. This is 2022, not 2002.

P.S.: After disabling always-on private - the session was pulled back automatically. At least this I can appreciate from Firefox.