I will shortly post two screen prints, for FF and IE8. (It would be nice if screen prints could be uploaded with the original question.)

I'm using FF29 to access https://developer.mozilla.org/en-US/Add-ons/Overlay_Extensions/XUL_School/The_Essentials_of_an_Extension . The span tags from the HTML are showing up in certain text boxes, and make the text very difficult to read. The text sometimes briefly displays correctly on initial page load, but in a few seconds, when all the css is applied and the font changes, the span tags show up in the text. I can display the page in IE8 and don't have this problem. It this the result of some setting? I notice that there is a notification inserted at the top of the page about a recent security breach. I wonder if insertion of this notice is throwing off some of the subsequent page content? I will shortly post two screen prints, for FF and IE8. (It would be nice if screen prints could be uploaded with the original question.)