You can create your own Theme with the Firefox Color Plugin.

The plugin seems unable to affect the colour of the search bar or search bar text.

The same question is unanswered at https://support.mozilla.org/en-US/questions/1376134

You could try changing this preference in about:config to Dark (0), light (1), system (2) or browser (3). layout.css.prefers-color-scheme.content-override

If that doesn't work, try creating the following preference as a number and make it 1 for dark mode (0 for light). ui.systemUsesDarkTheme

https://support.mozilla.org/en-US/kb/about-config-editor-firefox

You didn't share a screenshot like the other thread linked above, so this might not be relevant, but...

That can be caused by older versions of the MaterialFox theme for userChrome.css and may require a manual tweak. https://www.reddit.com/r/firefox/comments/ujrbyg/ff_100_white_address_bar_on_default_theme/

You didn't share a screenshot like the other thread linked above, so this might not be relevant, but... That can be caused by older versions of the MaterialFox theme for userChrome.css and may require a manual tweak. https://www.reddit.com/r/firefox/comments/ujrbyg/ff_100_white_address_bar_on_default_theme/

That worked! I deleted the chrome folder and user.js, restarted firefox and everything works like normal now. Thank you!