After updating Firefox to Version from version 17 to 18 via automatic update it displays the following error message when trying to vists SSL sites ( via HTTPS://)

“The proxy server is refusing connections”

After rolling this back down to version 17 with the installer it starts to work again

We do use a proxy onsite provided by Network Box with no authentication.

I have had to disable automatic firefox updates via , to stop it updating

Select “Tools” and “Options” and wait for the pop-up window to appear. Choose “Advanced” and “Update.”

*** Update *** 21/01/2013

Known Firefox Issue : http://support.mozilla.org/en-US/questions/946573

Firefox 17 Links

http://www.mozilla.org/en-US/products/download.html?product=firefox-17.0.1&os=win&lang=en-US
http://www.mozilla.org/en-US/products/download.html?product=firefox-17.0.1&os=osx&lang=en-US