Mozilla is currently testing an update process for those people who will be making major updates (such as from Firefox 1.5.x to Firefox 2). They currently activated the new process for people who are upgrading from one nightly build to another nightly build.
The reason they are doing this is because some people don’t like to update to the latest software, heck, some people are still using Firefox 1.0.x! For that reason they don’t want to constantly bug people to upgrade to the latest version which is why they allow people to choose “Never” to upgrade to the latest major release.
The “Update Available” screen:
The license agreement (not exactly completed) 
Now that’s one license agreement i’d be glad to accept!
Also, is it just me or is it weird that only the “T” in NOT is underlined?
It’s a “hotkey” (or access key…I’m having a brain cramp and can’t remember what it’s called).
Just like how the “c” in “accept” is underlined.
What a COOL news for all system administrators!
Now I can tell all the folks that they have to press [Get the new version] button, and they are up-to-date with their browsers all the time, forever!
Assuming they have Firefox 1.5 installed, because Firefox 1.0.x don’t have the updater.
I just checked for my nightly and this screen came up. The download was 7 mb!
The download is 7MB because you are essentially re-downloading ALL of Firefox…which is what people upgrading to a major version will have to do.
What a bummer…
Yeh, 7MB, takes hours
I know people still on 1.0.x – it’s not because they don’t want the new versions, but because they don’t know about them. I’m very much liking the modern trend of being able to update your products – it’s even better when you can set them to update in the background, because even though I wouldn’t, it’s good to set it when I install stuff on a person’s PC that I know they’ll never update.