My site is behaving inconsistantly using theme Blogs Mu

Through your support I have suppressed the two banners for this
theme using CSS code
#header, #top-content {
display: none;
Today this is working intermittently. If I look at the site from Chrome, it still has the banners, but from Firefox it hasn't, though at one stage it did and when I deactivated the simple-custom-css plugin and reactivated it, it work ok again. But not on Chrome, even thoug I have been deleting the cache to make sure any changes were reflected.

This has started happening since I have been configuring the Membership plugin today. Not sure if that has any relevance, but perhaps?

Thanks for any help with this.