The Nightly build (22.0a1) is updated daily and has the latest code fixes and thus may be unstable.
This version is meant for experienced testers only to check out new code and to see if it if working properly before it will be added to a release version, so it may be faster to some extend.

You should always install such an alpha (Nightly or Aurora) or beta release alongside of a the current release in case of problems (a lot of times websites may be broken).

• http://kb.mozillazine.org/Testing_pre-release_versions
• http://www.mozilla.org/en-US/firefox/channel/

Hmmm, I'm not sure if it's fair comparison. Today's "nightly" is the future Firefox 22, so naturally it is quite evolved from today's release version (Firefox 19).

I understand the that Nightly is a test browser and may be unstable, but I seem to prefer the way the downloads are presented in Nightly over the way they end up on the released version of Firefox. The arrow next to the Home Button is to me an improvement, especially the way it lights up green when a download is finished, plus I think the download box is an improvement too. I was just curious on why those things are changed when the released version comes out.

https://blog.mozilla.org/channels/2011/07/18/every-six-weeks/

The arrow next to the Home button will show up in Firefox release in Firefox 20. All features that are in nightly will eventually show up in release, when they are ready.

Rage, there are multiple channels of development.

Release is currently 19.0
Beta is currently 20.0b
Aurora is currently 21.0a2
Nightly is currently 22.0.a1

When 20.0 is released the versions moves/merges to the next channel and Nightly will have 23.0a1 start in development.

Aurora and especially Nightly get checkins pretty much every day so therefore a update each day. They are meant more for devs and Testers.

What you see in the current 22.0a1 Nightly build you have may be pretty much the same or close to when 22.0 is a Release down the road.