Duplicate buttons in theme menu

[cnieuweboer]

Description
The buttons in the Firefox theme menu show 2 buttons overlapping. Both are functional and have their own mouseover animation.

Screenshots

Tweaks in use
Default in a new profile

Additional context

[Lockframe]

The settings/addons page has not been touched due to Mozilla constantly updating those pages with each release. They will be overhauled only after Mozilla's 'Nova' redesign is released and stable to avoid constant breakage.