Crossrider apparently offers a toolkit others can build into their add-ons, so it might be difficult to identify the culprit by name. One options would be to just disable everything that isn't essential and restart Firefox to see whether that helps.

You also could try some other scanners. These two tools are highly regarded:

Malwarebytes Anti-malware : http://www.malwarebytes.org/products/malwarebytes_free

SUPERAntiSpyware : http://www.superantispyware.com/

However, if they change Firefox files they could damage your settings, so I recommend backing up your Firefox settings in case something goes wrong. See Back up and restore information in Firefox profiles. (You can copy your entire Firefox profile folder somewhere outside of the Mozilla folder.)

Finally, I saw this old thread. Maybe it's related to your problem?

can't remove completely crossrider's google+facebook. Some entries in about:config stay there upon unistalling and restarting

Hello Plugin1,

Sorry to hear about your issue.

It's important to understand that Crossrider is a development framework used by many developers to create cross browser extensions, and is not an application on its own.

You have probably installed a browser extension that was developed using our framework which we are not affiliated to it except for providing the development solution.

To remove it from your computer simply follow the steps in the FAQ: http://crossrider.com/pages/faq#uninstall

Regarding the search.crossrider issue you are describing: we have never encountered or heard of such thing, can you please reply with more information, prefreably screenshots to better explain what you are experiencing.

Crossrider is very keen about end-users security so we would be happy if you can provide us with more information to address your issue.

Yours, Shmueli Ahdut Crossrider Founder & CTO