When using Firefox on a PC unwanted text boxes may appear in the WYSIWYG editor.  These text boxes contain the letters "AB" in them.  They also seem to multiply every time you save the page, snippet, item or whatever you are working on.  Even if you delete them, they come back when you save.

This issue is caused when an older version of Skype (4.1 or older) is installed on a PC which already has Firefox on it. When Skype is installed it adds a "Browser Highlighter" plug-in to Firefox.  It is this plug-in which is causing the problem.  

The solution is to disable the plug-in. To disable the plug-in go to Tools>Add-ons in Firefox and "The Browser Highlighter" plug-in should be listed there.  Click the disable button for that plug-in then close and restart Firefox.  You should then be able to delete the AB Boxes and they won't come back.