Contend does not work in IE. ([if !supportEmptyParas] [if !supportLists] problem)

Hello,

i just did an awful lot development on a new site.
Today I tried it out with IE (usually I use firefox).
I edited the content with TinyMCE.
When I look at the content with IE i see lines such as this:

or this:

·

I use the Spreadfirefox theme (modified).

I could really use some help with this. Where do I look to make this work correctly.

Thanks
Andre