Hi! jmckitrick, First of all you should have to know about the differences between these browsers. :) Firefox has a stable version which get updated after a certain period. Currently it is 32.0.1then the Firefox beta is the next version which will be released as the Firefox stable with the best features on the next update then Firefox Aurora and followed by Firefox Nightly! The Nightly browser gets daily updates so you can hope for the latest feature comes first in Firefox Nightly then Aurora then Beta finally implemented in the stable version! So if you prefer the latest features I will suggest for the Aurora. (You can choose nightly too but it is mainly for the developers purpose!)

As far as the speed is concerned nearly all the browsers have the same speed (That's what I observed and it is my personal experience!)

If you have to ask, stick with the Release version.

When a "speed improvement" enters the development stream, typically it hits Nightly channel first, and then progresses to Aurora, then Beta, and finally Release. Occasionally, a Bug fix that affects "speed" may land on Aurora and Nightly at the same time - depending upon how important it is to other features that have progressed to Aurora.

IMO, the biggest difference in speed for most users is how many extensions they have installed. Few extension developers support anything but the Release version, and maybe the Beta version near the end of the 6 week Beta period in the development process. So not as many extensions are compatible with Nightly and Aurora, and once you get to the Release stage Firefox may seem slower, but that is usually due to having more extensions installed that "suck the life out of Firefox" in comparison to the Alpha versions.

If you're going to experiment with different versions, please make sure you have a separate Profile for each - to minimize issues resulting from minor incompatibilities that may crop up between the different channels from time to time. http://forums.mozillazine.org/viewtopic.php?f=23&t=2821799

I guess my question was mostly focused on debug information, optimization settings, etc in Nightly and Aurora. I thought perhaps the binaries themselves might be slower, but I wasn't sure, so that's what I was asking about.

All things being equal, all channels will be the same speed. In reality, because new fixes and features land in nightly first, it may be faster than other channels, and that speed improvement will filter down until it hits release.

As others said though, since you have to ask, you probably should just be using release.

The Firefox Nightly has the most new code to add new features, so that version has a larger file size, but the developers are adding all kind of optimizations to speed up the program and possibly different files are used like the logins.sqlite file that is now also being used in the current release to store the passwords instead of the signons.sqlite file. The localstore.rdf file will also disappear and is replaced by the xulstore.json in current Nightly builds. Because of such changes it is vital to always use separate profiles for each version.