IE vs Firefox

[Timbow]

Is IE 100% ok for GetSimple ? Some part of my site are not displayed on IE but everything is ok on firefox.

It isn't really a GetSimple issue. GetSimple will generate html as specified by the theme and plugins you are using. Some theme authors have gone to great lengths to make sure their sites display properly in IE but some don't seem to even test them in different browsers. Even validation of the html doesn't guarantee that IE (especially older versions) will display a site correctly, and if you are using windows XP you can only use old versions of IE.

So the problem is the same as for any web design. GetSimple doesn't solve the issues or create any new ones that I am aware of.

As for your site I don't know what the problem is, but check the head section of the template for the doctype, the html shiv and the normal <!--[if lt IE 7]> stuff and proceed as normal.