'Classic' css tweaks for Firefox 57+ v1.0.7

Changes since v1.0.6

[Buttons]

• (new/experimental) squared button appearance for classic buttons on navigation toolbar
• (tweaked) back/forward buttons > custom appearance (for above new option)

[General UI]

• (tweaked) short findbar on top
• (new) increase general font size (might break some items, if a too high value is set manually)

[Location Bar]

• (fixed) autocomplete popup > classic popup attached to location bar
• (new) dark background color for location bar and searchbar