Window resizing and position doesn't persist
I am using Thunderbird 140.8.0esr (64-bit) on Kubuntu 25.10 multi-monitor configuration. New install, very little customization.
Thunderbird will not retain the window size or position for the main window or messages. I have have tried deleting both the xulstore.json and session.json files (one at a time and both). When I delete the xulstore.json file and restart Thurderbird, it starts maximized. When I set the position manually e.g. to use about 90% of the screen for the main window and about half the width and about 90% of height for a message window and then close Thurderbird I can see the new window size vales written into xulstore.json e.g 2493 x 1362 and 1501 x 1317 "messengerWindow":{"sizemode":"normal","screenX":"0","screenY":"0","width":"2493","height":"1362"} "messengerWindow":{"sizemode":"normal","screenX":"0","screenY":"0","width":"1501","height":"1317"}
When I close and restart thunderbird it reverts to opening in the center of the primary monitor at a smaller size than when I closed it. The values in xulstore.json have changed to 960 x 540 "messengerWindow":{"sizemode":"normal","screenX":"0","screenY":"0","width":"960","height":"540"} "messengerWindow":{"sizemode":"normal","screenX":"0","screenY":"0","width":"960","height":"540"}
I found a similar recent question if this helps with a possible solution: https://support.mozilla.org/en-US/questions/1527783 but I cannot locate the referenced userChrome.css file to see if there might be something similar to try.
I am also using a multi-monitor setup. If I move the Thunderbird window to the second screen and close it, it always re-opens on the primary display at the 940x540 size. Thanks!
Opaite Mbohovái (1)
Since no replies... in case it helps anyone else; I ended up using KDE Window Rules to force Thunderbird's main window and message window to a specific size and position. Position Thunderbird where you want, right click the title bar and select Configure Special Window Settings (You might need to click More if you don't see this option). Window Class: Mail thunderbird_thunderbird Window Role: 3pane (this may be different for you depending on how you have your view set up) Add Size and Position Rules to apply initially. e.g. position 8000 x 0 and size: 1600x 2000
Open a message (any message) and position as you like. Repeat the process to add a rule for the messageWindow. I only added size so the windows did not stack on top of each other if I open multiple messages at one time.
The class and role should be filled in for you; all you really need to do is add the size and position rules.
Window Class: Mail thunderbird_thunderbird Window Role: messageWindow size: 1900x1800
.kwinrul exports for full details ``` [Window settings for thunderbird_thunderbird] Description=Window settings for thunderbird_thunderbird clientmachine=localhost position=8000,0 positionrule=3 size=1600,2000 sizerule=3 title=Inbox - my@email.com - Mozilla Thunderbird types=1 windowrole=3pane windowrolematch=1 wmclass=Mail thunderbird_thunderbird wmclasscomplete=true wmclassmatch=1 ```
``` [Window settings for thunderbird_thunderbird] Description=Window settings for thunderbird_thunderbird clientmachine=localhost size=1900,1800 sizerule=3 title=YA Message - Mozilla Thunderbird types=1 windowrole=messageWindow windowrolematch=1 wmclass=Mail thunderbird_thunderbird wmclasscomplete=true wmclassmatch=1
```
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