If you cannot uninstall/remove that client, probably a content of Mozilla Firefox is missing, Look in Appdata both Local - LocalLow - Roamming. If a Mozilla firefox content is still there, it should work before uninstalling it. Make sure you have Mozilla as trusted program in your firewall. This problem mostly happens when it file is missing. Thank you for the report.

See:

• https://support.mozilla.org/kb/Websites+look+wrong
• http://kb.mozillazine.org/Error_loading_websites

Reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• Press and hold Shift and left-click the Reload button.
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (MAC)

Clear the cache and the cookies from sites that cause problems.

"Clear the Cache":

• Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do not click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes