- problems loading the font file where these icons are defined, check the browser console for errors.
- some extension that destroys the CSS styling. Try making a clean copy of the app without extensions and then add them one by one to see which one causes this.
Oh, and you should run the app with the browser console open and caching turned off. I have written a small document on how to troubleshoot extensions Troubleshooting your extension. Perhaps I should rename it to 'Troubleshooting anyones extensions'.
Hope this helps