Missing thread icon?

Today it seems that at least one of the icons used in front of threads has gone missing, maybe more.

Here’s one example - note the missing icon in front of the topmost thread:

Here is another missing icon in front of a thread I haven’t posted in:

This is using Mozilla Firefox 3.0.13

The same problem doesn’t seem to exist in Internet Explorer 7.

Maybe it’s a problem with Mozilla Firefox 3.0.13 (which I upgraded to today), and not the forum? :confused:

EDIT: Oh my - it’s a problem with the AdBlock Plus plugin in Firefox! :doh: