sIFR displaying different sizes in IE and Firefox

[rcshield]

Hello WebmasterWorld:
My sIFR headers are displaying in different sizes in IE 7 and Firefox 3.

How do I get my sIFR headers to display in the same size? I am using pixels to define the header sizes in my CSS file. Should I switch to em, percentage or something else? I appreciate your expertise.

[edited by: eelixduppy at 12:53 am (utc) on June 17, 2009]
[edit reason] snipped URL - please describe issue [/edit]