It would be nice if the HTML formatting in the HTMLEditorExtender was the same as in the old HTMLEditor. The HTMLEditor is using span tags with styles instead of font tags (font tags are deprecated by W3C). And the HTMLEditor format the HTML as XHTML.
Comments: Under the hood, the HtmlEditorExtender uses the HTML5 ContentEditable attribute to enable rich formatting. Each browser implements formatting in different ways. For example, when you click the Bold button when using IE then the HtmlEditorExtender generates <STRONG> STRONG tags. When you use the HtmlEditorExtender with Chrome, then <B> B tags are generated. Each browser generates different HTML. I've created a new feature request for the HtmlEditorExtender to do post processing on the generated markup so that markup can be converted into a canonical form. If you want this feature, please vote for http://ajaxcontroltoolkit.codeplex.com/workitem/27159
Comments: Under the hood, the HtmlEditorExtender uses the HTML5 ContentEditable attribute to enable rich formatting. Each browser implements formatting in different ways. For example, when you click the Bold button when using IE then the HtmlEditorExtender generates <STRONG> STRONG tags. When you use the HtmlEditorExtender with Chrome, then <B> B tags are generated. Each browser generates different HTML. I've created a new feature request for the HtmlEditorExtender to do post processing on the generated markup so that markup can be converted into a canonical form. If you want this feature, please vote for http://ajaxcontroltoolkit.codeplex.com/workitem/27159