Other browsers doesn't apply :active when the using the right mouse button.
Created attachment 22505 [details]
When you click using the left mouse button, the background turns green. When you release it, the background reverts to white (as it should).
Using the right mouse button makes the background green too (which it probably shouldn't, as the other browsers don't do this), and releasing the context-menu by typing escape or clicking in the menu-bar makes the background stay green. Only by release the context-menu by clicking inside the window makes the background revert to white.
Browsers tested: Firefox 2 mac + win, Camino 1.5, Opera 9.1 mac, Opera 9.5 win.
IE7 doesn't seem to support :active at all.
Bug is in r35401, nightly downloaded 2008-07-27
Confirmed with r40778. This is also reproducible when right-clicking on a button, for example.
See also bug 29818.
…and bug 24427.