After the v91 update, all websites look different. Stylesheets are loading, but background images do not. Buttons are not styled. Text is always black. Links are always blue. It's like the website's own CSS is selectively ignored in favor of some sort of bland default. None of the following have fixed the issue: 1- View Menu > Page Style is set to Basic Page Style. I've flipped this to No Style and back. CSS is rendering, just not correctly. 2- I restarted FF in safe mode (option-click to launch). 3- I trashed the prefs.js file. 4- The problem still exists in Troubleshooting mode. 5- I cleared the cache. 6- I switched to the Dark theme. 7- I removed all extensions and add-ons (other than whatever comes with the browser). 8- I reinstalled v91 from a fresh download. This problem breaks FF internals; e.g. see the screenshot of the About:config page, where a popup is transparent because (presumably) its background isn't rendering.