IMPORTANT: These locations changed again in Firefox 21. See this post.
If you are running into problems with Firefox 14 not honoring values in you set the default preferences, it's because Firefox preference files have moved from defaults/pref to defaults/preferences and your files have to move as well. (See bug 779437.)
Apparently custom changes to the default preferences were supposed to be there all along, but no one actually knew that (not even Firefox).
So when you are creating JS files for your autoconfig settings or to set the various add-on scopes values, make sure they are in defaults/preferences. (You'll have to create this directory.) Note that this method works fine on Firefox 10 as well. I'll be updating all my posts as I have time.
On a separate note, the CCK is broke on Firefox 14 - it's not creating bookmarks properly. I've tracked the problem down to a Places change, but at this point I am unable to work around it. I've contacted the developer that made the change that broke me, but I haven't heard back. Hopefully he'll be able to point me in the right direction.
I can't stress this enough. PLEASE test on Aurora and Beta if you have the bandwidth to do so. These Firefox 14 issuse should not have been found after Firefox 14 was released. And yes, I'll admit that I've been failing in my testing as well, but to be blunt, I'm not paid for any of the time I spend on enterprise, so it's not one of my top priorities.