Unable to resize thunderbird window

Solution 1:

Same problem here (Ubuntu 18.04, Thunderbird 68.10.0). Maximise-option is disabled, horizontal adjustment too. Problem does not occur in newly created profiles. When switching back to original profile, problem is still there.

Found a quite effective work-around: In Thunderbird, try switching to the CardBook-Tab (Thunderbirds addressbook plugin) via Extras --> CardBook or Strg + Shift + B

Maximise-Button will reappear until next program start.

Solution 2:

Your comment (search in profile directory) led me to this answer.

I had exactly the same problem since yesterday (26th September). Thunderbird window was suddenly a little bit too big on its right side. Couldn't reach maximize button which was off screen. Could move window thanks to sliding it, thus got back access to maximize button, but it has no effect. When clicking on "Resize" of system menu, can try to resize horizontally but it actually doesn't change. Resizing vertically worked normally.

Did you also install the CardBook extension? flex's answer indicated that this is a possible cause, and it is in my case too.

After many tries, I finally found that renaming the file xulstore.json fixed the issue.