Since upgrading to F38 thunderbird won't start maximized nor does remember the y size of its window.

Reproducible: Always

Steps to Reproduce:
1. delete xulstore.json to be sure
2. start thunderbird (it starts maximized to the left half of the screen)
3. press the "maximize" button or resize the window manually
4. restart thunderbird

Actual Results:  
thunderbird starts not maximized (or whatever the last size was), not even half-maximized

Expected Results:  
thunderbird starts maximized (or whatever the last size was)

When resizing the thunderbird window by drawing it to the maximum x and y sizes, thunderbird remembers the x but not the y size.

Removing xulstore.json didn't help.

Using Gnome and Xorg.