Is it possible to make firefox save browse history on ram?

I think you need to be looking at Firefox's cache...I think that is is where all that temp stuff is actually stored, not your ram.

This from about.com
Every browser, including Firefox, has a place where they store bits and pieces of websites that you visit - images, ads, scripts, etc. - so that the next time you visit that particular site, you will see the page load quickly. This is called a cache, and Firefox gives you a coupla options here. As we did before, navigate to Tools, Options, Privacy, and then Cache.

* The general rule of thumb on the cache setting is to have it no larger than 60 MB (that would be 60,000 KB), unless you have an immensely huge hard drive with lots of memory. This is just a good general setting. I have it set for 60 MB on my main machine, and 50 MB on my laptop, since my laptop is kind of a memory weenie (sorry, Lappy!).

* One more thing about cache - if you for some reason want to get rid of everything, you can click Clear All there at the bottom of the window. Every single thing you've been doing on the Web will be gone if you do this - history, cache, cookies, passwords, etc. - so consider carefully before hitting the confirm button.

*If you export your bookmarks this should not be a problem. Hit clear and close your browser, let it set a couple seconds then FIRE it up again, (lol I couldn't resist) import your bookmarks and start logging in to your accounts (to CACHE the info) reset your home page(s) and restart. You should have a clean cache then. Although, it will get cluttered again as you go on, but this is something I do about every 30 days to catch some of those sites that I have accounts with but don't frequent much but have a 30 day login cache.(my note)

And that's pretty much it for cache settings. You can get really technical here again, just like everything else we've gone through so far, but these settings are just fine for the general user.