The ReportViewer control displays reports in IE almost always correct and in other browsers almost always incorrectly. The DOCTYPE is most likely the problem.
The default Visual Studio 2008 template code for webforms generates a DOCTYPE of
aka XHTML 1.0 Transitional. Only IE support this.
Change it to something more ordinary like HTML 4.01 or earlier
and the funky display problem (squished columns, failed controls, etc) may disappear.