What? You were going to switch browsers because you were having problems using a beta or nightly version? I have an idea... Use the release version!
It's 2016 now so maybe it's time to upgrade your box and it's 4 GB of RAM.
EDIT: How is Firefox eating up to 3Gb of RAM on your machine? I never seen mine go over 1.5GB and that's been after a week of not closing it (64-bit version/no Flash installed).
Personally, I would reevaluate how you use browser.
I just restarted FF an hour or so ago, and haven't even had it reload most of the tabs that used to be open (FF restored them, they're just not loaded yet as I haven't tabbed to them), and I'm already at 1.5GB resident with probably 15 active/loaded tabs.