Highlight unfocused tabs

[Xembie]

It would be useful if unfocused tabs are highlighted with their matched color.

[etiennewan]

I'm not sure this is feasible at the moment with the current theme API, pinging @nt1m to be sure about it
But I agree, that would be awesome !

[nt1m]

Not possible atm, requires https://bugzilla.mozilla.org/show_bug.cgi?id=1320585