Firefox's Gmail Checker version 1.2
Mon, 23 Jun 2008
Gmail Checker version 1.2 is now available. The sound notification bug was fixed at last. I've also added a debug window (see screenshot) so that you can see what the extension's doing in the background. From now on if you want to report any problems, please include the debug messages* as well.
You can download it directly from my website (here). It should be available at addons.mozilla.org in a few days.

(*) these messages may contain your private, personal, blah, blah information, so remember to mask the details out before sending me (not that I care anyway, but in case...).
Gmail Checker v1.1
Sun, 13 May 2007
Hey, long time! I've got over my laziness to release beta3 of the Gmail checker extension. The new feature added is sound notification although Firefox has refused to play any wav file on my machine except the stupid beep.
On a side note, a new FAQ on Pidgin/Gaim's website was plain flaming. Geez, I've compiled Gaim 1.5 and every beta release of its without a hitch on my Slackware box.
Update (3 June)
Version 1.1 is out finally.

Gmail Checker version 1.1
Sat, 20 Jan 2007
New version of the Gmail Checker extension is available now, though I've made it as a beta release first since there were some significant changes. It now uses the new SQL storage of Firefox2 to keep the configuration information, and you can also mark a mail as spam via the extension instead of going to Gmail. The latter feature was implemented to save me some seconds going to Gmail just to report spam.
A lame screenshot:

Update (14/2/07)
Beta2 is available. New features can be referred from this post's comments. There were no bug fixes. I feel proud.
Firefox extension: GMail Checker
Tue, 15 Aug 2006
Currently available Gmail manager extensions for Firefox don't work as I like so I wrote another GMail Checker. It works with Firefox v1.5 up to 2.0. Well, technically, it should work with older versions as well, but these contents.rdf files make me sick so I dropped support for those legacy versions.
My extension page on addons.mozilla might take a couple of days to be online, though. It's available here (edited on 3/9, that was a long approval process).
Does anyone read manga? You've got to check out 20th Century Boys, man. Urasawa's works sure are excellent.