Sorry but the tab codes didn’t work for me, but the plugins work perfect.
With it I inspect the Startseite, but first it didn’t work. I have to inspect the Startseite background in the customize tab and then I found out the id of it. (screenshot of it)
The active tab has at the moment a white background with the plugin Classic Theme Restorer. With it you can change the background color of the active tab. This plugin I have installed because I use a Windows 8 theme for windows 7 and firefox had a problem with this theme. (see screen) So I have to use Classic Theme Restorer with the settings: "Remove tab toolbars background fog (Windows AeroGlass)" to fix the green background on top.
Now all works perfect.
I have my good old Windows 7 with a Windows 8/8.1 theme and a Firefox with a Windows 8/8.1 design. (see screen)
I’m using these Stylish codes:
#nav-bar {background: linear-gradient(rgba(255, 255, 255, 100), rgba(255, 255, 255, 100)) !important;}
#personal-bookmarks {background: linear-gradient(rgba(255, 255, 255, 100), rgba(255, 255, 255, 100)) !important;}
#PersonalToolbar {background: linear-gradient(rgba(255, 255, 255, 100), rgba(255, 255, 255, 100)) !important;}
And the plugin Classic Theme Restorer to get the active tab white.
Thank you for your help