It completely locked up Firefox on Ubuntu 20.04, rendering a frame and making a single beep sound about once per second. Had to close the browser and force kill some processes to get the TTS to stop.
I had a beeping issue on Firefox 81 running on Windows 10. The weird thing was, the beeping noise continued even after I closed Firefox. There were some OS updates pending installation, so I just chose to reboot/install instead of troubleshoot further.
> Unfortunately, Mozilla still hasn't fixed the performance bug 1190398 around ShadowBlur, filled for BLCK4777 5 years ago