Uninstall non-loaded extension from Safari

Question

When opening Safari I get this error:

Now I want to uninstall this extension, however it doesn't show up in the Extensions preferences:

How do I uninstall this?

Answer 1

That doesn't look like an extension, but a SIMBL Plugin.

These can be found in the directiory /Library/Application Support/SIMBL/Plugins, and you should be able to remove the SafariOmnibar.bundle from there.