The fact that such an extension exists, and that it may get broken again in later versions, says a lot about what Mozilla really think of customisation.
Oh? And what is that? "Customization is great and you should have the option to do so"? Try having a "classic theme restorer" with Chromium.
> it may get broken again in later versions
Future changes may cause incompatibilities in any project. That is why such changes are released in major new versions so that add-on developers have plenty of time to make adjustments and fixes.
It is supposed to get Chrome extension support this year too, and if I ever had the time I'd try to expand their sync options (currently Opera + Chrome) to sync tabs and such.