I have opened a ticket where the server is hosted, and asked them if that file locking could be possible. And referred them to this topic. The underlying library, is compiled into the mod? I couldn't see a separate dll for it. Firefox , yeah can be a pita. I suggest to create a new profile, https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles You can just create a new one, and see if it helps, before deleting the old one. And besides that I noticed firefox to crash lots on some flash ads. Really annoying stuff, if you have to incorporate those ads on a website and your browser is constantly crashing, after 2-3 refreshes of the site. edit: They replied, Since I couldn't rename/delete that file (cause its windows server), I suppose ET had it locked for its own use.