Click to show and hide Acrolinx in your Firefox toolbar.
If you click to show Acrolinx and the icon turns red , it means that you can't use the Sidebar on that page. Try to show the Sidebar on a different page.
If you've set your browser language to English, German, French, Japanese, or Swedish, then the Sidebar will also appear in this language. For all other languages, the Sidebar will appear in English. If you need to, you can change the language in the advanced settings.