+++ This bug was initially created as a clone of Bug #1674000 +++

Consider making these changes for Ubuntu as well.

[Environment]: Ubuntu 18.04.5 LTS
latest Nightly 84.0a1 2020-11-13
Firefox 83.0RC

[Preconditions:]
Go to System Settings - Universal Access - Set High Contrast to ON

[Steps to reproduce:]
Start typing in address bar and select an engine to open Search Mode.

[Actual results:]
Search mode chiclet colors don't match high contrast theme.

[Expected results:]
Chiclet colors follow high contrast color scheme.

[Suggested severity:]
S4

Your screenshot doesn't look bad to me. It's pretty legible, but the contrast between the two blue colors could probably be increased. Do you know or have a suggestion for what the colors should be?

I would expect it to look more similar with Windows chiclets in high contrast mode, as in spec, but I agree that it would suffice to increase the contrast.
As for the colors, maybe #0060df and #00d0df?

That's not a spec though, it's just a screenshot of what the colors happen to look like on Windows's version of high-contrast modes (I made the screenshot). I don't think there's any reason the Linux colors have to look similar to the Windows colors; the important thing is that the contrast is sufficient. That said, in addition to at least increasing the contrast between the two blue colors, we could also look at using standard system colors for the indicator in high-contrast Linux the same way we do in high-contrast Windows. I'm not sure whether there's a query for Linux corresponding to the @media (-moz-windows-default-theme: 0) one for Windows, though.