This question is little different from preventing an application from stealing focus, rather how can I find out what the heck is stealing focus?
It goes like this. I'll be typing something in Firefox on Vista (as I am now). Every few minutes something else is stealing focus. It's not because a window is moving to the foreground. The change is somewhat subtle in window in the foreground takes on the attributes of a de-selected window (e.g., menus slightly dimmed), but it's most notable when typing, as the keys I type are no longer sent to that window. It also makes it extremely annoying.
How can I track this bugger down so I can remove it?