I'm not sure at all about that. I've not been running the betas recently. I used to download nightly builds, but haven't had the time to do thorough testing for the build, so I've been running the stable branches of FF and TB.
I'm pretty sure that the FF equivalent to this TB release (1.0.7) is a part of the stable branch that is very different from the Beta branch (codenamed DeerPark), so I'd not be suprised if the Beta branch of TB was similarly different.
I found one big difference. The Beta version I have been using has spell checker as you type, much like MS Word. I like that feature and the new non Beta release doesn't have the feature. Thanks for the information.