You can download it here https://www.mozilla.org/en-US/firefox/new/

Firefox has a current release, and three versions in development: Beta, Aurora, and Nightly. For regular daily use, the release version is best (most stable). However, if you want to experiment with future capabilities, you could try one of the others.

If you have accumulated valuable settings such as bookmarks or saved passwords, please make a backup of your profile folder before experimenting with development versions. Users often reporting losing/corrupting their setting unexpectedly, especially with the Nightly version.

Related article: Manually back up and restore Firefox profile data

Note that the Aurora (currently has 33.0a2) and Nightly (currently has 34.0a1) development channel builds get checkins almost every day so they get a update each of those days. This can sometimes lead to regressions or issues where the fault checkin(s) may need to be fixed or removed.

Also you should not share the same Profile between the Release and Aurora Builds.

Make sure that you create a separate profile for each developer version if you decide to give them a try.

See these mozillaZine KB articles for information:

• http://kb.mozillazine.org/Testing_pre-release_versions

• http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows
• http://kb.mozillazine.org/Shortcut_to_a_specific_profile
• http://kb.mozillazine.org/Bypassing_the_Profile_Manager

Create a desktop shortcut with -P "profile" appended to the target to launch Firefox with each profile. Set in the profile manager which profile is the default profile to use when you click a link in an external program to make sure that the default browser opens with its own profile.

You can add -no-remote to the command line to open another Firefox instance with its own profile and run multiple Firefox instances simultaneously.

• http://kb.mozillazine.org/Opening_a_new_instance_of_Firefox_with_another_profile

See also:

• https://developer.mozilla.org/Mozilla/Multiple_Firefox_Profiles