Firefox 10 is out and add-ons are now Compatible By Default. As reports are coming in that some add-ons are not working, I wanted to write a quick note on how this feature plays alongside the Add-on Compatibility Reporter (ACR) extension. In short, the ACR settings that make add-ons compatible are themsleves not compatible with Compatible By Default in Firefox. So these settings have been disabled in ACR, and the extension acts now only as a reporting tool. To put it another way, ACR no longer makes old add-ons work, deferring completely this task to Firefox.
Compatible By Default does not enable all extensions. The types not enabled include the following:
- Add-ons marked to work with a Firefox version less than 4.0
- Add-ons with binary components
- Add-ons explicitly marked by the author as incompatible, i.e. opt-out of Compatible By Default
- Add-ons tested and determined to not be compatible with a given version of Firefox, and marked as incompatible by Mozilla
UPDATE (See Blair’s comments below): Add-ons installed by 3rd party software are enabled if you opt-in, which is a feature introduced in Firefox 8.
The original aim of ACR, hence ‘Reporter’ in the name, was for users to inform authors if their add-on did or did not work. I would still encourage you to install it and if an add-on degrades Firefox in any way then please use the reporting mechanism (Compatibility button on the add-on listing) to let Mozilla and the author know.
Note that ACR also works with Thunderbird and Seamonkey.