Can't find untested extension in order to remove it: SafariTabSwitching
Generally, Safari plugins should be in /Library/Internet Plug-ins/



However, I discovered SafariTabSwitching is actually in a different location

Source : Safari Tab Switching FAQ


  How to uninstall?
  Remove this file: /Library/Application Support/SIMBL/Plugins/SafariOmnibar.bundle
  Alternatively you may download this uninstaller and run it. Note that uninstaller won't remove SIMBL Agent as you may use some other SIMBL plugin and we don't want to break them.