Gtk-Warning, Theme parsing error after removing the extension

[ghost]

I installed and removed the extension through the Firefox-Gnome-Extension.
Unfortunately, when I now start programs from the terminal, I get the following message:

(firefox:2377): Gtk-WARNING **: 13:37:45.450: Theme parsing error: gtk.css:1:118: Failed to import: Error opening file /home/user/.local/share/gnome-shell/extensions/no-title-bar@franglais125.gmail.com/stylesheet.css: No such file or directory

(firefox:2377): Gtk-WARNING **: 13:37:45.450: Theme parsing error: gtk.css:2:124: Failed to import: Error opening file /home/user/.local/share/gnome-shell/extensions/no-title-bar@franglais125.gmail.com/stylesheet-tiled.css: No such file or directory

So it seems that somehow the extension was not properly uninstalled. There seems to be some things remaining in the system that shouldnt be there. Is there a way that I can fix this warning on my machine?
I hope this is the right place report this.

[ghost]

Removing the corresponding entries in ~/.config/gtk-3.0/gtk.css fixes this issue.