I had the same thing with the siteadvisor (and WOT) in firefox and I never gave it a moments thought as it had never displayed anywhere else.
However I have ditched the siteadvisor add-on as it simply isn't a reliable resource now with it giving wildly differing results from other similar add-ons, reporting some as bad that aren't and some that are good which are plainly wrong. Add to that being a dial-up user it also throttled my browsing bandwidth. So for those reasons it is history on my system, nothing to do with aesthetics.