Waterfox Nova style, and an Appearance panel.

Automatic Waterfox look. In Waterfox the popup switches to a style modeled on Waterfox's Nova: pill-shaped controls, rounder cards, and Nova's light and dark palettes. Detection uses runtime.getBrowserInfo(), which needs no permission.
Appearance panel. The half-filled circle next to the Password/Passphrase tabs opens it:
Style: Auto (Waterfox look in Waterfox, Firefox look elsewhere), Firefox, or Waterfox
Mode: System, Light, or Dark
Theme color: Waterfox's twelve, from Default to Pine, for the Waterfox style. The popup can't detect which one you picked in Waterfox, so choose it here.
Readable in both modes. In light mode each theme color uses a deeper shade, because the pastels barely show as checkboxes or focus outlines on a light background. Tests check all twelve for 4.5:1 text contrast and a 3:1 focus ring in both modes.
No flash on open. The popup restores the last look before it first draws, so it doesn't open in the default style and then switch.
Fix: the presets row no longer shows through under panels that hide it.


No changes to password or passphrase generation. 67 tests pass, and web-ext lint reports 0 errors, 0 warnings, and 0 notices on the packaged zip.