I have this same problem with Webmail 1.3.10 and GMail 0.6.5 (and 0.6.6b1) - with GAFYD.
I use these extensions with multiple Thunderbird profiles. I have the problem with only one of them. (I know that GMail and GAFYD provides POP service and the Webmail extension is not required if you can use POP through any firewall.)
