When I open the Mail & Newsgroups Acount setting, change some preferences, as the signature, and press Ok. the next time I open the preference the change is not saved on version Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:0.9.6+) Gecko/20011211
I have the same issue on 2001121303 on XP. Specifically, for the past several days my newsgroup posts have been in HTML format because the "compose in HTML..." won't stay unchecked. Moz will also not remember to use my signature file. Then today I noted that mail sending isn't adding domain information to recipients as it used to. Another mail pref "remembering" type bug was fixed a few days ago; I'd thought that would correct this but it doesn't seem to have.
After dealing with several such bugs, I have to make this one as a dup of bug 113682. Work around suggested there : Please check you prefs files and make sure that integers and boolean values are stored without any quotes around them (i.e., change "10" -> 10, "true" -> true) to make your appp work properly. That bug (which is fixed a while ago) was caused by unitentional base prefs changes. For more history follow updates in bug 113682. *** This bug has been marked as a duplicate of 113682 ***