Windows not getting focus

[cyberslag5k]

I've noticed on a number of systems that sometimes when I switch from one maximized window to another, the new one will appear to pop up, but will not be focused. I'll actually have to minimize the window I'm working on to get to the window I want. I run Windows XP pro, and the majority of these windows are instances of firefox. Perhaps that might be the cause, I'm not sure.

Has anyone else experienced these annoyances, and know of any way to fix them?