Why do you have a profile w/ 1600 tabs in it. If whatever it is is so important, aren't you afraid to lose it? I'd be terrified that one time Firefox just wouldn't shut down clean.
This is why Firefox stores a sessionstore file. _And_ a backup of that sessionstore file. And a previous version of that sessionstore file. And a backup of the file as of the last several times you did a browser update.
The idea is to never lose the session in an irrecoverable way.
At one of my jobs, they instituted weekly scheduled reboots of desktops; after several times of getting my sessions killed by that, I started making an effort to close everything at the end of the day; I don't always close all my tabs, but often, and I never leave more than two or three. Whatever was interesting, but I couldn't read, I don't worry about -- if it's important, it'll probably come up again; I just leave a couple things open if there's work I need to do on them when I get back.
Other times I'll find something and think; I'll read that later.
Or. Less often, I'll be recurring into different things looking for solutions to a problem I have. Eventually I'll find something relevant and close the tab that was last opened, I forget the others and they become orphaned in my like of tabs I'll likely never get back to, until my browser crashes hard and I lose everything.
After the mild panic a wave of relief washes over me, and I go about my business hoarding tabs once again.
For the second, we all do that, but again, the optimal thing there would be to have some extension or tool that keeps track of your "to read" list.
As for tabs stacking when you're looking for a solution, that's generally what my comment referred to. I know somewhere in those 20 tabs, there's one for the documentations to the function I'm trying to use, but it's honestly faster to search for it again than look at those 20 tabs for it.
This context is useful if I get sidetracked/distracted by a coworker, so I can retrace why I was looking at a certain page.
Of course not all browsers have that feature, but Firefox does. So finding the tab you want is pretty easy.
Session Buddy works well for Chrome (and it's really needed there). Firefox is much more reliable IME, and I haven't needed a backup in many years, but I still use SendTabURLs, as it makes finding and bulk closing tabs easier. There may be better options for Firefox, but I haven't needed one so haven't gone looking (used TabMixPlus years ago though).
Tabs are just much more convenient bookmarks.