To reproduce: 1. Fetch trunk build 2. Try to compose a mail Results: Nothing happens and this error appears in JS Console: Error: uncaught exception: [Exception... "Could not convert JavaScript argument - 0 was passed, expected object. Did you mean null? arg 4 [nsIMsgComposeService.OpenComposeWindow]" nsresult: "0x80570035 (NS_ERROR_XPC_BAD_CONVERT_JS_ZERO_ISNOT_NULL)" location: "JS frame :: chrome://messenger/content/mailCommands.js :: ComposeMessage :: line 255" data: no] One thing I found while taking a quick look at the code was is that the call unter http://hg.mozilla.org/comm-central/index.cgi/annotate/0137db13395c/mailnews/base/resources/content/mailOverlay.xul#l33 has eight parameters, not seven. Maybe this is the cause of this bug here (fallout from Bug 366482).

I can't reproduce this using: Build identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1a2pre) Gecko/20080825002620 Mnenhy/0.7.5.20005 SeaMonkey/2.0a1pre With this Build I have composed new E-Mail Messages, replied to some, and replied in Newsgroups too, everything works like expected, no error in Error-Console.

Hrm, after rebuilding it also works again. I still think though that the code mentioned in Comment 0 is wrong.

I've tried this on latest trunk with no issues: Build identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1a2pre) Gecko/20080825002620 SeaMonkey/2.0a1pre But you are correct, it does have too many parameters (though the patch that was reviewed has the right number!) Thanks for the catch - fixed by http://hg.mozilla.org/comm-central/index.cgi/rev/a508be333305