hi, you can find all the known fixed security issues at https://www.mozilla.org/en-US/security/known-vulnerabilities/firefox/ - not all of them are depending on javascript. i don't think that there's any existing evaluation of what's the exact risk under the parameters you've provided nor anyone will go through the hassle of figuring this out for an outdated version.

what's keeping you from updating?

Firstly, thank you for replying.

I cannot speak for anyone else but for me personally, this new version of Firefox is a step backwards in both looks and in functionality.

Looks aside for the moment, because I can live with the superficial stuff, but when on You Tube for example, where as before I could play 1440 resolution videos with ease, I am getting playback issues with all of them! F5 to refresh will work 90% of the time, but not all!

Hi, looks can be changed a few million ways with usserChrome

• https://www.howtogeek.com/334716/how-to-customize-firefoxs-user-interface-with-userchrome.css/

fyi : Audio / Video

• https://support.google.com/youtube/answer/91449?hl=en
• https://support.google.com/youtube/topic/3014746
• https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues
• https://support.mozilla.org/en-US/kb/html5-audio-and-video-firefox
• https://support.mozilla.org/en-US/kb/fix-video-audio-problems-firefox-windows