When writing an e-mail, I can't attach files: a click on the button “📎 Attach” has no effect, nor does choosing “File(s)…” via the small arrow ⌄ to the right of this button, nor does choosing the menu item File > Attach > File(s)…. The variable mail.compose.attach.dir is set to /tmp/e-mails (this directory doesn't exist). Disabling the Add-Ons and changing the locale don't help. Changing mail.compose.attach.dir to /tmp does help.

There seem to be bug reports elsewhere: https://bugzilla.mozilla.org/show_bug.cgi?id=2077590 and https://bugzilla.mozilla.org/show_bug.cgi?id=2077526. As the functionality is severely reduced for me and the bug affects others, too, I've raised the severity of this bug report. Please patch the version in Debian trixie.

a/o today 2026-10-21 Tbird 140.17.0esr in Deb 13 stable all up to date has stopped attaching files to emails.
No process will work.
The only workaround I've found is to use Caja, select the file and choose 'send to' w/ email which will open a new send
message window with the attachment.
If I have already begun a message, I cannot attach anything.