Not sure what IE7 for Linux actually is built around, but I know I've experienced issues after upgrading Firefox on some of my Linux machines. The plugin used for both Server and ESXi is incompatible with newer versions of Firefox (NPAPI change?). Read http://communities.vmware.com/message/1462526 for similar issues described.
How I got around it was just installing a second version of Firefox (3.5) on my machine and using that for accessing the server where ESXi was installed.
