I tested this with the current settings:
* Linux elementary OS, based on Ubuntu 18.04.2, GTK 3.22.30
* mail.tabs.drawInTitlebar set to `TRUE`
* HiDPI monitor at 3840x2160 with scaling factor `DISABLED`
**Thunderbird 72.0a1**: Closing and reopening maximized works with all the themes. ✔️
**Thunderbird 68.1.1**: Closing and reopening maximized works with all the themes. ✔️
**Thunderbird 60.9.0**: Closing and reopening maximized works with all the themes. ✔️
Which version of GTK are you running?
I wonder if that might be related. Does it happen with Firefox as well?
I know Magnus runs Ubuntu, but I don't know if his version of GTK is more up to date.
I tested this with the current settings: drawInTitlebar set to `TRUE`
* Linux elementary OS, based on Ubuntu 18.04.2, GTK 3.22.30
* mail.tabs.
* HiDPI monitor at 3840x2160 with scaling factor `DISABLED`
**Thunderbird 72.0a1**: Closing and reopening maximized works with all the themes. ✔️
**Thunderbird 68.1.1**: Closing and reopening maximized works with all the themes. ✔️
**Thunderbird 60.9.0**: Closing and reopening maximized works with all the themes. ✔️
Which version of GTK are you running?
I wonder if that might be related. Does it happen with Firefox as well?
I know Magnus runs Ubuntu, but I don't know if his version of GTK is more up to date.