Check first http://docs.moodle.org/en/HTML_editor_FAQ
Can you send some more info about your site - address for example?
but I don't think they should break editor. You have obviously just copied and pasted some content from Microsoft products...
One possible reason could be in your browser - some malware or phishing program or some partly functional plugin. Have you tried other browsers elsewhere (in addition to your current browsers) ?
I could not test the editor with guest access but you could try to turn debugging to ALL from site administration and check possible errors. At least normal source did not show any signs of injected code.