Comment 207 for bug 187313

@Mitchell:
> in fact there seem to be a bug in the firefox 3 code, so the menu should
> not be released when the right button is pressed, it should be showed
> when it is released
Just to clarify -- the quoted chunk above isn't quite accurate.

The timing of context-menu-appearance in firefox 3 is actually correct (and it matches Firefox 2) -- Firefox is *supposed* to show menus on mouse-down, not on mouse-up. This is how all GTK apps behave, including e.g. nautilus. (right-click on your Gnome desktop, and you'll notice that the menu appears on mouse-down there as well)

That's why installing MouseGestures is a workaround, but not a source for a true fix. It avoids this particular bug, but it moves Firefox away from "correct" GTK behavior by delaying the menu's appearance until mouse-up.