Tap here to go to the mobile version of the site.
Your Firefox is out of date and may contain a security risk! Upgrade Firefox

Support Forum

When opening firefox, it always says 500 internal server error.


Whenever I open firefox to its home or any other web site, it only provide 500 internal server error. This error does not involve manual proxy configuration.

Have also removed and download firefox 4 and still does the same thing.

Firefox was downloaded only 3 months ago.

Additional System Details

This happened

Every time Firefox opened

This started when...

Late in December

Installed Plug-ins

RealPlayer, RealJukebox, Hulu Desktop, Shockwave Flash, Cannon iMage Gateway, Silver Plug-In, Bing Bary, Micorsoft Office 2010, Windows Live Photo Gallery, Real Player VideoShim


  • User Agent:

More Information

FInstalled Plugins: Mozilla default plugin is enabled
Rest able.

  • Top 10 Contributor
  • Moderator
10738 solutions 96600 answers
  • "Clear the Cache": Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now"
  • "Remove the Cookies" from sites that cause problems: Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Troubleshoot Firefox issues using Safe Mode to check if one of the add-ons is causing the problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

  • Don't make any changes on the Safe mode start window.


aquarin 0 solutions 2 answers

Helpful Reply

This worked for me. It seemed one of my add-ons called "Relevant Knowledge" was the culprit. I'm not even sure what this add-on is or when I even installed it. But it doesn't appear to be necessary as Firefox is working fine for me now.

tflash2612 0 solutions 1 answers

Helpful Reply

It is the "Relevant Knowledge" Add On. It's Spyware. If you disable it and restart FireFox it'll allow you to browse again. Then you'll want to do how to remove it.

EHow suggests just uninstalling from control panel > Uninstall programs. http://www.ehow.com/how_5634500_remove-relevant-knowledge-spyware.html

I suggest you download Malware Bytes which has saved my butt a few times. Reason being, I've also seen a few threads which suggest you must remove this from your registry. Perform a quick scan firt. Then full later. I'm running one now and it's alredy found a couple (28) of issue from this "Relevant Knowledge Spyware."

Also, this is how it was installed on my machine. I downloaded a "Free Flash Video Converter" from LEAWO.COM and installed their software. That's when it was placed onto my cpu. I can verify that 2 other machines in my office were infected when downloading this software from their company. Advice is to stay away http://www.leawo.com until they shape up. Their software was great though.

Note: One employee when downloading, was prompted by her anti virus that something was amiss.