I had problems with the TMC-2012 on my old firefox on my work linux computer. Due to glibc issues I can't upgrade past Firefox 3.6.24. I switched to the other option and it works fine.
Can you track down the source of the problem? Maybe upload a screen shot? The only real code difference that a browser might care about is the hack for the header images and the Google search bar.
I will poke around and upload a screenshot after lunch. It took a bit to switch back as I had trouble with a number of features. Give me 40 minutes or so.
Interesting, but likely off-topic so I'll restrain from directly asking for more 'color' on this topic. [Aren't they on version 14 by now?]
Firefox is dynamically linked versus a library glibc provided by the linux installation. Newer versions of firefox require newer versions of glibc to be installed and fail to start on older linux boxes.
How much "older" when you say "older linux boxes"? Windows 3.0 era, Windows 98 era, or somewhat newer?