If we need to force users to repeatedly "buy in" to disabling extension compatibility checks on a per-version (3.6, 3.6b, 3.6p(re)*, etc. ) basis, I think we should do so in a much more friendly manner. My UI experience today: 1) Google around to find out why my extensions are broken 2) Create a new about:config key with "3.6pre" 3) google around to discover that I needed to set it as "3.6p" due to a bug 4) Notice that I now had four separate "checkcompatibility" settings, from previous version upgrades. Try to delete the obsolete ones. 5) Google around to learn that to delete an about:config setting, you have to "reset" it, than restart the browser (!) 6) Mutter unprintable things under my breath, and worry about declining goodwill in our nightly/beta user community. It would be a much better UI experience if I could simply open the Add-ons manager, see that my add-on was marked as "disabled", and have a button labeled "Force enable" that would enable it. (Yes, we could have a scary pop-up that warns the user that they should know what they're doing, etc.). Perhaps even better would be some sort of screen that pops up when I first upgrade (or am upgraded without my asking, actually) to 3.6pre or whatever, noting that "The following extensions may no longer work: click the box to force them to be enabled" or whatever. IMO it would be fine to only provide these pop-ups in beta/nightly versions, so we'd be providing them to an already relatively sophisticated base of users. I'm not trying to advocate that we allow a "force this to work" button in regular releases.
I really don't think it should be easy to force compatibility since doing so can break the browser. Having UI to accomplish this implies that we approve of this action.
We already have things like Nightly Tester Tools and the Addon Compatibility Reporter that provides the sorts of behaviour you're looking for. I'd rather suggest people use tools like that rather than work on anything that would only be useful to nightly users right now. What we can be doing though is improving the dialog you get shown at startup whenever you start a new version of Firefox that has to disable some of your add-ons since clearly you didn't read it ;)