I have been fixing some IE7 bugs with my Ajax code lately and I am going to start documenting some of the problems I've encountered and their solution. These will be tagged crossbrowser. The first one is innerHTML. FF gives a different result than IE given the same dom structure. For example:
Right off the bat the case on the tag names is different. And secondly the attributes in FF is quoted while in IE they are not. For these reasons, it's not smart to do string comparisons on the innerHTML of elements.