The problem with playing around with Firefox 3 is (by default) you can't run both Firefox 2 and 3 at the same time since they both insist on using the same profile and insist on running only 1 copy of Firefox at any one time.
Want to get in on checking out the new features but still want good old Firefox 2? Here's how:
First, you should create a new profile just for testing Firefox 3. You should do this to keep your precious Firefox profile safe from any problems in Firefox 3. Otherwise, Firefox 3 will use your current Firefox 2 profile by default. You can create a new profile easily with the Profile Manager, which you can access by running:
/path/to/firefox -profilemanager -no-remote
Create a new profile (I gave it an obvious name, 'minefield', which is the codename of the current Firefox trunk). If you get confused, the official Firefox website has more detailed instructions on how to create a new profile.
- Now, you should already have one of the Firefox nightly builds. If not, you can download the latest nightly build from the Firefox nightly build directory. You can start up Firefox 2 normally (just so you can see Firefox 2 and 3 running side by side). For Firefox 3, we're going to start it differently.
We're gonna run Firefox 3 using our newly created profile. I'd written earlier on how you can run two Firefox profiles at the same time, and you can still do the same with Firefox 3:
/path/to/firefox3 -P minefield -no-remote &
The 'minefield' in the command is the name of the profile we created earlier. Windows users should leave out the '&' (on UNIX-based systems, this just runs Minefield in the background so that you can exit your terminal).
Firefox 3 should start up with your new clean profile!
That's the Firefox 3 (Minefield) icon living right next to my Firefox 2 icon in my dock (yeah, I use a Mac).
Just so I can put up another screenshot (as if I needed to prove that this really works), here's Firefox 2 and one of the recent Firefox 3 nightly builds running side by side: