As a complement to Firefox, you might like an extension that enables vertical tabs. I use Tree Style Tab, use of which can become complex; not for you.
Simpler extensions include Visual Tabs. Two screenshots:
This is a terrible change for me. I always have loads of tabs open and this change forces a lot of concentration just to find the different tabs.
My first action after seeing the new design was looking for themes that improve the readability of the UI and the only working solution I found was disabling “browser.proton.enabled”.
Addition: The new tabs also eat more vertical space. Why?
Hmm, it seems it works! Here are my 2 custom styling files (enable toolkit.legacyUserProfileCustomizations.stylesheets option in about:config and extract the chrome folder from the archive into your profile folder): http://popov654.pp.ru/chrome.css