Just a few weeks after the first release of Firefox Aurora, Mozilla's "developer's" build of Firefox, the browser maker debuted a switch that lets users switch on the fly among Aurora, Beta, and Release versions of the browser.
Released in today's Aurora update (download for Windows | Mac | Linux), the benefit of the built-in channel changer is that users who want to see what's coming in future versions of Firefox can now do so without having to download a separate installer. Change the channel and restart the browser, and the version that opens ought to be the new channel.
Mozilla noted in a blog post that the switch points to a mirrored copy of Aurora as the Beta release. An actual beta release is expected in the coming weeks. Choosing the Release version of Firefox currently makes no changes to the browser, likely because Firefox 4.0.1 was released before the channel changer code was introduced.
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To change Firefox channels, you must first be running the Aurora version. Go to the menu button, then Help, and choose About Aurora. The first sentence below the version information reads, "You are currently on the Aurora update channel. Change." Click Change, and the window shows the change channel drop-down. Choose the new channel you want to use, then select the Apply and Update button below.
When Firefox restarts, it ought to be running the new channel you've chosen. You can confirm this by going back to Help, then About. Mozilla has explained more about how the channel changer works in an article on its site. The channel changer does not affect your profile, so your tabs and other settings should all remain the same.