As for this 3.6 Beta1, there is a dedicated extension, ‘Add-on Compatibility Reporter 0.1′ which seems most appropriate :

QUOTE:

“After installing the Add-on Compatibility Reporter, your incompatible extensions will become enabled for you to test whether they still work with the version of Firefox or Thunderbird that you’re using. If you notice that one of your add-ons doesn’t seem to be working the same way it did in previous versions of the application, just open the Add-ons Manager and click Compatibility next to that add-on to send a report to Mozilla.

Even if your add-ons all work fine, if they’re marked incompatible, please let us know that they work fine by submitting a success report so we can encourage the add-on developer to update their compatibility information.

We’ll collect all of the reports and let add-on developers know what users are having problems with, or if their add-ons seem to work just fine in future versions of the product.

If you encounter problems and want to disable your incompatible add-ons again, uninstalling the Add-on Compatibility Reporter should revert to your previous compatibility checking settings.”

‘Add-on Compatibility Reporter’ is available at : https://addons.mozilla.org/en-US/firefox/addon/15003

I’ve downloaded Firefox 3.6 Beta 1 and will test it with this ‘Add-on Compatibility Reporter’ extension.

https://addons.mozilla.org/en-US/firefox/addon/6543