Separate Issue; Your System Details shows;

Installed Plug-ins

Adobe Shockwave for Director Netscape plug-in, version 12.1.3.153 Adobe Shockwave for Director Netscape plug-in, version 12.1.2.152

Extensions

Firefox OS 2.2 Simulator 2.2.20150330.1-signed (fxos_2_2_simulator@mozilla.org) Firefox OS 3.0 Simulator 3.0.20150526.1-signed (fxos_3_0_simulator@mozilla.org)
Having more than one version of a program may cause issues. You must remove the older programs. Then get the current full installer.

Shockwave Director: Shockwave Standalone Installer / Uninstaller{web link} Shockwave Director Version 12.2.0.162 http://get.adobe.com/shockwave/

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.

Thanks!

If you use a proxy and that proxy sends its own certificate to Firefox then you will have to get the root certificate of that proxy and install it in the Firefox Certificate Manager. If you have this certificate in another browser then export it there and import the certificate in Firefox. You need to set at least the trust bit for websites to make the certificate work as a trusted root certificate. You can contact the proxy site and ask them for a link to their certificate if you trust that website for using it via a secure connection because the server sees all data if they decrypt and re-encrypt your data before passing it to the destination server.

• https://en.wikipedia.org/wiki/Proxy_server

Open the "Add Security Exception" window by pasting this chrome URL in the Firefox location/address bar and check the certificate:

• chrome://pippki/content/exceptionDialog.xul

In the location field of this window type or paste the URL of the website.

• retrieve the certificate via the "Get certificate" button
• click the "View..." button to inspect the certificate in the Certificate Viewer

You can inspect details like the issuer and the certificate chain in the Details tab of the Certificate Viewer. Check who is the issuer of the certificate. If necessary then you can attach a screenshot that shows the certificate viewer.

Thanks! Turns out I needed to add burp's certificate to FF.

Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution more easily.

Thank you for contacting Mozilla Support.

I think it was because I forgot to add Burp's SSL certificate to FF, and I did not realise that I had to press the "Forward" button to send the request on Burp. But I think it was cor-el's answer that would work for similiar programs.