Switching themes in only IE increases font.

Switching themes in only IE increases font.

For starters, I'm kinda new to using JQuery. But bear with me. 

I have several themes I've downloaded, as well as a theme switcher ( http://bitly.com/RBot89) that I'm using to switch back and forth between themes. 

My problem is that only in IE, the fonts in the tab element increase, it also affects everything that is inside that tab element. I'm not having this issue in FF or Chrome. 

I re-downloaded the themes with 1em as the font size, as opposed to 1.1em, thinking this would alleviate the issue, but to no avail. I've stepped through every line in the JS above, and thought I've pinpointed the issue, but once I took my debug messages out, it still persisted. 

Has anyone else had a similar issue, or know the root cause to this? Or can anyone point me in the right direction as to how to solve this?