Unless Firefox developed an allergy to your computer's graphics driver software overnight, it's hard to explain. But let's check for any customized settings:
Here's how you can check on that:
(A) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.
More info on about:config: Configuration Editor for Firefox. Please keep in mind that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.
(B) In the search box in the page, type or paste webgl and pause while the list is filtered
Firefox should list numerous preferences for WebGL
(C) Scroll down and check for any preferences that are bolded, indicating that they have been customized. You can restore the default value using the reset button (leftward arrow) at the right end of those rows.
