This worked fine for years until I updated firefox and thunderbird recently. Now, however, when I click on a link in an email in thunderbird, rather than open the indicated webpage in firefox, nothing at all happens. network.protocol-handler.app.http in tbird's about:config specifies the executable /usr/lib/thunderbird/open-browser.sh and running the latter at the CLI with a URL as an arg does work as expected: the spec'd URL is loaded into firefox. So I suspect a bug in tbird. Anyone else having this problem?