I won't be getting off XP, so lets take that as the premise.
Found the problem....
Seriously though. XP supports 4GB RAM max, something that gets utilized quickly these days, even if all you're doing is web browsing. Not to mention XP support has been officially dropped and most other third party developers have quick developing and supporting it as well.
I'm the kind of guy who can get above 600 tabs so my main concern is that it handles memory well and doesn't start falling apart when you get up to a huge number of tabs.
What in the actual, flying, other-worldly frack are you doing on that machine?
NO ONE should ever be using 600 tabs. Period. Doesn't matter the OS or the browser. Bookmarks exist. Use them.
I don't want to update because its too much of a hassle given how I have everything set up and, outside of the browser stuff, everything works great.
Also I have my GUI very fine tuned because I sit very far from my monitor and so I have to have it modified in a way where fonts are made very big in everything and to customize all that over again in another OS would be a pain.
By the time you figure out this browser issue you'd already have invested more time than just setting up the updated OS. 
Dude. I get it. XP was great. Change is scary. You've got your stuff set up the way you like it. So on and so on. But it's 2016 and support has completely stopped for XP at this point.
It's seriously time to shit or get off the pot. Either buck up, and stop using a ridiculous number of tabs, and stop complaining of issues with a essentially deprecated OS;
OR get with the times, and move on. It won't be that impossible to set everything up again.
The only thing stopping you from fixing your problem here, is you. Staying with XP for these reasons, given the "requirements" you have for your machine usage, makes
zero sense.
