Browsing takes up too much memory leading to stuttering

This is a common "issue" people have been running into since Firefox went the way of stupidity. Firefox and I think Chrome as well as its derivatives are mostly fine tuned via the registry or Group Policy for enterprise users. You can read about that here. You can control things the hard way or the easy way with an extension here. Its code is here.

Now, having the ability to actually "control" Firefox is withen your grasp. Unfortunately, I don't see an option to change memory usage. I did read this and it appears the memory usage can somewhat be lessened via the click of a button in a about:config Pref. So you'd enter about:memory in the address bar and you'll find the Minimize memory usage button in the middle of the other buttons. Testing this myself I don't think it was very much. You could also stop caching data in memory as well and just use the disk. I don't use memory or disk cache at all and haven't seen a performance hit, but some may and it may cause a slow down. Go to about:config in the address bar, accept the crap verbiage, and search for memory. Now find the browser.cache.memory.enable Pref and set it to false. This is called a "boolean". You can read about the Pref here. Don't monkey with anything else unless you absolutely know what you're doing.

All of the Prefs use the prefs.js file which you can read about here. If you would like to backup this file for testing or what ever, then you can easily find it in your Windows AppData folder for Mozilla.