I have noticed that when you are administering themes, and happen to have >= 8 themes that have their own configurations (thus tabs), the tabs overflow into the sidebar. I have messed around with firefox to remove the following attributes from the CSS to make it work:

ul.secondary {
border-collapse:collapse;
/*line-height:normal;*/
list-style-image:none;
list-style-position:outside;
list-style-type:none;
/*white-space:nowrap;*/
}

After commenting out the two mentioned above, the configuration tabs were no longer overflowing into the sidebar. However, not knowing the Theme/CSS that well, I did not know if this would backfire given there are other unordered lists on the site (or will be with your data). Just thought I would point this out to you guys!

Thanks,
Jason Cameron