I've noticed this for years 😳, but I figured I should finally report it. Restore Window Positions successfully restores every window size, position, and monitor except Thunderbird (and that includes its sibling program, Firefox). I switch between 4 monitors in the office to 1 or 2 monitors using Remote Desktop. For some reason, Thunderbird comes back squished when I restore to the 4 office monitors, as if the width were being ignored. See the attached. Left is actual result and right is expected previous size.

Sadly, not so quick. Tomorrow I run remotely and Friday I will be back into the office to see the error. Will test on Friday.

The answer is... yes. The first time I press the retore button, DF moves Thunderbird to the proper monitor with the proper x-y position of its upper-left corner. I waited for repositioning to end, then pressed the restore button again. DF then restored Thunderbird's former size.

HTH!

PS: It appears the issue occurs only when I am using two monitors remotely, my 2012 Macbook Pro (retina) plus 1920x1200 DELL monitor in portrait mode. I brought the Macbook to work Friday, but couldn't reproduce the error. Monday I used both monitors remotely with Remote Desktop, and Tuesday morning when I returned to the office to use my four monitor setup, I reproduced the issue.

I could swear this started working with Beta 4(!), but I will pay attention the next time I run the failing scenario next Tuesday and report then.

Fixed! <dancing in the streets> The issue can be closed.