There is no documentation at site :/

I think the main thing you need to say is that FireGPG does only INLINE, although I believe I was able to decrypt one OpenPGP/MIME encrypted message sent from a POP mail account.  I have not been able to repeat that feat though.  Maybe I confused the Thunderbird window with the Firefox window (they do look very similar) because at the time I was VERY tired. I have four WebMail accounts (for testing various things) and two pop mail accounts and have been testing this plug-in extensivle using only my own key.  I really do think you need to say you are using INLINE.  It took me a while to deduce that.

Other than that, I don't feel any burning need for documentation, and I must confess I can't understand you saying that Yahoo and HotMail aren't supported.  Just because there isn't a button, all people need to do is select the text and use the Tools -> FireGPG options of encrypt  or verify in going through those two WebMail programs.  AOL will NOT work with FireGPG.  They bring up that panel / window making it impossible to get to the menus. But if somebody is using Evolution for their POP mail account (it is the default MUA for IMAP & POP mail on Ubuntu Linux), they won't know why the two won't interoperate.  People need to be told that the POP person will need to use INLINE.  But I do feel that your major thrust needs to be for Windows.  One person told me that they needed WinPT.  I don't think that is necessary, but it is necessary to tell them how to add the ";%ProgramFiles\GNU\GnuPG" folder to the path to be sure gpg.exe can execute.

Good JOB!