peterparseghian said

unresponsive script or error message unable to connect.

Post the full error message you are seeing.

There is security software like Avast and Kaspersky and BitDefender and ESET that intercept secure connections and send their own certificate.

http://www.ehow.com/how_11385212_troubleshoot-reset-connection-firefox.html

https://support.mozilla.org/en-US/kb/server-not-found-connection-problem

https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message

https://support.mozilla.org/en-US/kb/connection-untrusted-error-message

http://kb.mozillazine.org/Error_loading_websites

This Connection is Untrusted is sometimes caused because the computer system clock is wrong. Check the time / date / time zone settings.

Hi Fred, I have visited each site that you recommended and have done what they suggested with no luck unless I totally missed something. Most sites simply will not play video or audio, they do play in Chrome. My internet security is with McAfee. The "unresponsive script " is not related to this problem. YouTube does give the following error message..... Unable to connect

Firefox can't establish a connection to the server at ad.doubleclick.net.

   The site could be temporarily unavailable or too busy. Try again in a few moments.
   If you are unable to load any pages, check your computer's network connection.
   If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the Web.

What should I try now? Thanks for your help. Pete

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. Is the problem still there?

Start your Computer in safe mode with networking. Then start Firefox. Try Safe web sites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Working through safe mode I was able to identify the problem as Adobe Shockwave Flash plug-in. I uninstalled it from PC and reinstalled it to the latest version. My problem is that I have to keep it on "Never Activate" for video to play and that doesn't seem right. What are your thoughts? Should I worry about it?

I found this; Windows 8 and Windows 10 have built in flash players and Adobe will cause a conflict.

Hi Fred, yesterday I refreshed Firefox and the YouTube error message "Unable to Connect" came back, the same as above but this time I don't have Adobe Flash Player installed. I've worked through all the steps above and I must have fixed it some way without knowing it. Can you help?