We are all expecting to have Firefox 4 out, but meanwhile we can also do something to help to the development of some add-ons that are supposedly incompatible with the most recent version of one of the most popular web browser.
When we have a new version of Firefox or if we are testing the beta releases of the 4 version we may find that some of the add-ons that we were used to install are not compatible with the version of Firefox that we are using.
Add-on Compatibility Reporter is a Firefox add-on that will allow you to install any kind of add-on, even if it is not compatible with your current Firefox version, but the real porpoise of this add-on is that you can report if the add-on is working or not with your Firefox version.
So with Add-on Compatibility Reporter you can help the add-on developers to know if their add-ons work on later versions of Firefox, causing them to work on it and maybe we will have that add-on natively available for the upcoming Firefox version. This add-on is compatible with Mozilla Firefox 3.5 up to the 4.0 beta 6.
Web Link | Add-on Compatibility Reporter




