Ability to hide URL bar when unfocused in oneliner

It would be a great option if there was a way to hide the URL bar in oneliner until a user focuses on it by hovering so tabs get maximum space.

[This ](https://github.com/TRPB/FewerFox)theme is sort of what I had in mind, but the URL is completely hidden. The cascade theme has [this ](https://github.com/andreasgrafen/cascade#url-bar-customisation) functionality using flexbox however it [breaks ](https://github.com/andreasgrafen/cascade/issues/47) in windows.

The issue names the oneliner configuration and links FewerFox and Cascade's URL-bar customisation; start by locating the repository's oneliner styles and comparing those references. Done means the URL bar is hidden until hover or focus, tabs gain space, and the behavior does not reproduce Cascade's reported Windows breakage.

Written by the indexing model from the issue text.