Editor Button CSS
Normally, the editor CSS is dynamically loaded when the Edit tab is created by adding the rules to the end of the last stylesheet. But, if the web site uses a method to "suture" all its CSS files together, then it will only have 1 stylesheet. In most browsers, document.styleSheets[0] is read-only, so inserting rules 1-by-1 throws an error and breaks Javascript.
Fixed by rewriting clientscript/special_reset.js. The code is now also much simpler, faster, and easier to understand.