Getting 256GB because your browser leaks memory is crazy! Besides all that will do is delay the inevitable, you will still run out of memory it will just take longer.
At various times I've had several hundred tabs open in Firefox, and I've got "only" 16 GB on my Linux PC. Quick count right now it has 58 tabs open, and has been running since March 3. Not having any memory issues, though there have been times in the past when it slowed down and restarting Firefox fixed it - i.e. they've had memory leaks but have found/fixed them, then sometime later a new memory leak is introduced which is found/fixed in a later patch.
Not sure what you're doing that uses up memory so badly, maybe one of the sites you have running does something that leaks memory at a very high rate. If you could figure out which site that is you would file a bug report and maybe they'll fix it. Wouldn't that be worth it considering how much money you'd save not having to find a laptop that lets you stuff in 256GB?