Downgrade to Firefox ESR, see my answer on my own post: https://support.mozilla.org/en-US/questions/1338596

I share this, was hoping the new ugly indistinct and messy interface would grow on me, but the experience using it is the opposite! Is there a way to keep the updated version but get the 88 HMI or any good HMi? I am testing themes to see if any can improve the user interface a bit, but the core issue is that tabs and other interface parts seem to float into each other and is both hard to use and difficult to look at. I feel dyslectic. Some theme like this improve on the visual issues with color, the it still suffer from the lack of borders between elements. [https://addons.mozilla.org/sv-SE/firefox/addon/older-design/?utm_source=addons.mozilla.org&utm_medium=referral&utm_content=search Older desing by theDankoCZ]

Firefox doesn't care.