I’ve been a long time user of Firefox, and now with version 11 as has occurred with previous versions when you click on an email hyperlink mailto: a new window opens but the email form from GMail does not load successfully, and you will get a message that there is a problem loading, to try HTML mode, etc.. None of this works.
We are working on determining what the problem might be, but at this point it appears to be something from within Firefox that is causing the issue.
