Thunderbird 115 introduced a new look. I hate it. Not only does it no longer fit in with KDE Plasma, it lost functionality due to it’s new integrated search bar in the title bar.
So I went on a mission to fix it.
To restore the regular title bar:
Go into Settings > General > Language & Appereance and uncheck the Hide system window titlebar
To remove search bar:
Toggle toolkit.legacyUserProfileCustomizations.stylesheets to true in Config Editor (bottom of Settings)
Find your profile directory via Help > Troubleshooting Information > Profile Directory (or about:profiles in same page)
This directory should have lots of files e.g. prefs.js and places.sqlite
Create directory chrome
Inside that folder, create a file named userChrome.css with the below content:
#unifiedToolbar {
display:none !important;
}
Restart Thunderbird
Enjoy!
There is theme support for thunderbird so if someone makes a classic theme, you can just download and install it.
But depends on the level of changes you want to make… Maybe not all can be changed with themes?
If thunderbird’s theme support is like of firefox, then you can’t make a theme with these changes, because you can’t restyle the chrome, and you can’t affect any arbitrary about:config values.