Usually Windows 10 themes uses solid backgrounds (unlike Windows 7). Maybe I'm not understanding what you mean by opaque.

Could you possibly share a screenshot of the problem? This article has tips on capturing screenshots: How do I create a screenshot of my problem? Please cut out or blur any sensitive information in the image before attaching it to a reply.

I'd like actual tabs, not floating buttons.

You have two choices to reconnect and differentiate tabs:

(A) Use a temporary preference in Firefox 89 to revert the tab bar changes (B) Use custom style rules in a userChrome.css file to tweak the tabs to your own specifications

Since (A) is so easy, I'll detail that here:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) In the search box in the page, type or paste browser.proton.enabled and pause while the list is filtered

(3) Double-click the preference to switch between true (new Proton style) and false (old Photon style)

Since this was kept in just for testing, there might be some occasional glitches.

Thanks for your input. I tried (A) and the "button" look was gone, but I still have transparent tabs; just going to use a compromise and use a theme called Dream of Waves. It's pale with no graphic, so I can still read what each tab says. The thing that was causing me trouble (as marked on the screenshot) was that I couldn't easily read the tab text sitting over the Firefox logo, or any other background pictures from other themes.

I'll mark this "Solved", since I'm satisfied with the pale theme and the "button" tab appearance. Thanks again for your prompt responses!

Hey, You can use Photon Colors theme which reverts back the colors to previous versions of Firefox. Attaching a link below for the same. https://addons.mozilla.org/en-US/firefox/addon/photon-colors/