The most common problem, that is the reason of the mess on your website in IE9,  may be the way you create your articles or custom content.
Do you use Word for fromatting the text you want to introduce on your website?

If yes, note that Word includes MSO tags to the html file making the code difficult to read, it looks as follows:

The example website source:



We strongly recommend to use a standard notepad to copy/create the text you want to use on your website and then format it with joomla editor.
For those who don't know how to extend joomla tiny editor tools:
navigate to Extensions -> Plug-in Manager -> Editor - TinyMCE and select the extended functionality.