Actively exploited bug in fully updated Firefox is sending users into a tizzy Fraudulent tech-support sites cause Firefox to freeze while displaying scary message November 5, 2019 https://arstechnica.com/information...tched-firefox-bug-to-send-users-into-a-panic/
This is not the 1st time Mozilla has left less-severe bugs long time, they've long been lacking manpower. The article says Chrome also had been vulnerable, but glancing at the Bugzillas & MB blog, it seems Chrome was not as severely affected and fixed soon.
One of the beauties of using Sandboxie. Use SBIE to terminate the browser, and those exploits can't hold the browser open. Got to love it.