Toolbar icon color is wrong for "System theme -- auto"

[AvverbioPronome]

I think it's using the icon for the dark theme. It's supposed to use the dark or light one

• Temporary Containers Version: 1.9.2
• Firefox Version: 115.9.1esr (64-bit)

Actual behavior

Icon is light on light background

Expected behavior

Icon should be dark on light background

Steps to reproduce

1. set theme to "System theme -- auto"
2. look at the tab bar icon

Notes

This is entirely solved by using either System theme light or dark explicitly. I assume the right color exists as a css variable with the firefox shell, but I have no experience inspecting that.

[AvverbioPronome]