Dark mode

[mortenn]

Describe the problem and steps to reproduce it:

Search for an addon in thunderbird, such as "dark mode"

What happened?

A light mode web page with matches was shown

What did you expect to happen?

A dark mode web page with matches should be shown

Anything else we should know?

When I search for addons inside thunderbird, I get presented a non-dark mode webpage, which causes me discomfort. Certain eye problems don't deal well with light mode, so it would be good for accessibility if all webpages supported dark mode and followed user preference.