There have been a lot of questions about the support for Firefox 4 in Selenium IDE. We know that the current Selenium IDE v1.0.10 does not support Firefox 4. It is not a simple matter of bumping the maxversion to make it compatible. There are core technical changes that make the existing Selenium IDE incompatible. So, Selenium IDE v1.0.10 will never work on Firefox 4.
The good news is that we will release Selenium IDE v1.0.11 to work on Firefox 4 and we are working on it. We have already fixed several issues and yesterday I fixed the issue that prevented recording on Firefox 4. None of us use Selenium IDE a lot and we need your help to make it better. We need your help to try out the latest build of the next version and tell us if something is broken. Grab the latest copy from http://bit.ly/selenium-ide-latest ( click the Artifacts tab) and don’t forget to include the build number when you tell us if it is ok or you are facing any issues. The right place to report any issues is http://code.google.com/p/selenium/issues/list. If you want to let us know your feedback, feel free to stop by on our discussion group http://groups.google.com/group/selenium-developers. Please remember that we are all people who try to help you out in our free times and it would really help us save time if you try to make your bug report as complete as possible.