Rated 5 out of 5 stars
I don't know if this only happens to me or everyone, but even though I choose "Always override themes" option, tabs colors still disappear when I use custom themes. When I change to default theme, the colors come back.
I'm also using "Classic Theme Restorer", but I didn't enable any tab color function in that addon.
The FF and addons I'm using are up-to-date.