Restore the original theme color picking QuietFox behaviour

[TheGITofTeo997]

This was the main feature of QuietFox: basically it changed dynamically its main color based on the Firefox theme you selected. Since we always use the Nord Polar Dark theme we statically (and maybe stupidly) declared the colors in the code as to match its dark, but it will always stay dark.

It would be good to restore the original behaviour, for example if you select an i.e. mainly orange theme, QuietFox should adapt to it dynamically, matching the orange color.

This might be a complicated feature to achieve, but the original QuietFox repo might be a good reference to achieve this.

Refer to theme-adapted menus in this repo.

[TheGITofTeo997]

Because of the structure that Firefox themes have, this might not be achievable; not for all themes at least. Other themes apart from Nord Polar Dark may already work in the current state, but since it's impossible to know every theme's variable's name, this feature it's not achievable for now. The issue will however stay open.