Hi all, I'd be grateful for some help with themes. I've been using Firefox and this specific feature for years and never had any issues with it. On my new PC, themes are suddenly looking like they have only been partially applied. Every theme so far has done this, I've checked all the regular customization settings and I'm stumped. As you can see in the screenshot, the theme applies to the tab and search bar levels, but not to the top level that shows the page title and system buttons. I know it's a cosmetic issue but it is driving me mad. Is this a "feature" in a new version of Firefox to make themes look like this? It looks more like a bug to me :(

I'm on Windows 10, brand new install on a new machine, I've only synced my Firefox tabs/bookmarks etc but it already looked like this before I did that or added my usual extensions. Any help or explanation why it's like this now would be appreciated!