Using multiple instances of Firefox...

Firefox has a great feature called Profiles. You can use them to have multiple instances of a browser. If you wonder why would you use something like that, here are few reasons:

• you might want to separate professional from private browsing, or to have development or hacking environment distinctive from "usual" environment.
• you might want to try out some new plugin without messing up your existing profiles.
• you have large number of installed plugins that considerably slow down the browser, or can even make it unresponsive, so you want to group them in different instances.

When you start the browser by running firefox command, either from command line or from GUI launcher, it will find existing running instance of browser and activate it. So, in order to be able to run new instance you have to use command line option --no-remote. Also, to select other than default profile, use -P option. In case you don't give an argument to this option the firefox will start with profile selection dialog. In this dialog you'll be able to select profile that should be run, but you can also create new profiles and delete existing ones.

For the end, I mentioned in the introduction that in different profiles I use different plugins. But NoScript plugin I use in every instance as I regard it one of the most important security additions to the browser. I strongly recommend that you install this plugin too!