Firefox Beta is the build for those who like a little bit of jeopardy, but who don’t want to risk everything by trying out Firefox Developer, the early alpha build of Firefox. Firefox Beta gives you a sneak peek at the next version of Firefox six weeks ahead of its final release, offering a relatively stable build that’s not quite ready for primetime, but still pretty solid.
Whereas Firefox Developer installs as a completely separate application alongside your existing Firefox installation, Firebox Beta will replace the stable build. Should you subsequently wish to go back to the safer version, you’ll need to manually download the stable version and install it over the top of the beta build.
Confirm which build you have by selecting About Firefox from the Firefox menu or button (it’s inside the Help menu if using the Firefox button).
Check out the next version of Firefox before it's released.