I've already scanned the old threads with no progress so lets try again. I have a few tabs open on ff. Its working fine, it has NOT crashed. I can copy a link from an email in thunderbird and paste it into ff and a new tab will open to that page. I can click a link in a document and the tab & page will open. However if I just click the link in thunderbird - hey presto "Firefox is already running, but is not responding. The old Firefox process must be closed to open a new window." It seems TB is not handling the link properly (it always used to!) However the various TB "fixes" I can find are either inscrutable, wrong or just dont work. Has anyone fixed this?