Firstly, you need to know that this add-on is not compatible with the latest versions of Mozilla Firefox. If you’re using an older version of the browser, open the Add-ons menu from Settings and click the Remove button next to the plugin. After that, navigate to the official web page and install the latest version. Also, press the Ctrl + Shift + Delete key combination and clear all cache, cookies and temporary Internet files.
Note: As you can see in the reviews for Browser Highlighter, the users don’t recommend this add-on because it is causing many problems. Also, it is rated with 1 out of 5 stars.