Release = 14.0.1
Beta = 15.0b5
Aurora = 16.0a2
Nightly = 17.0a1

esr = extended-support releases, currently is 10.0.6esr
default = used by third-party or builds you built yourself for example.

The latest release of Firefox for Win7 is 14.0.1 You may either be using a shortcut that is pointing to the Firefox 14.0.1 install or Firefox 14.0.1 was still running when you tried to start the Aurora build. The Betas are kind of close to that of the Release Candidates of before Firefox 4.0. aurora: This is a new channel which has been introduced with the rapid-release scheme since Firefox 5.0; these builds reflect changes which also went into beta for the next release, thus making them available immediately, or which were deemed unsuitable for beta but safe for the following release (and, in general don't contain any string changes). nightly: The nightly channel allows you to update to every nightly test build that is produced with latest code from mozilla-central. Which Fx 17.0a1 is currently on. The Aurora and Nightly channels only get updates whenever there are checkins to the channel which is usually daily, especially with Nightly. These channels are not really meant to be used with one build for several weeks like a release build. There are for main channels Release = 14.0.1 Beta = 15.0b5 Aurora = 16.0a2 Nightly = 17.0a1 esr = extended-support releases, currently is 10.0.6esr default = used by third-party or builds you built yourself for example. The Aurora is not really meant for regular Firefox users as they should keep it as a separate install form 14.0.1 and use a separate Profile from 14.0.1. Also note that early next week the versions on the channels with move/merge to next channel as Firefox 15.0 will be out on Tuesday if all goes well. If you do test the Aurora builds, there will likely be no updates sent for a few days next week as the Aurora channel can sometimes be unstable for a while due to the common dash of dumping checkins on it at last minute.