The junk that people put on their PC's

So my wife has been complaining about slow performance on her laptop. I gave it a look a couple nights ago and tweaked some settings, but it didn't seem that bad; then she let me know the problem was specifically with her browser.

I woke up early this morning so I decided I'd give it a look. She was right; it was terrible. Firefox would take literally minutes to open a new page. What on earth was going on?

I fired it up in safe mode and looked at the extensions. Cooliris, check. Download manager, check. LinkedIn extension, check. Firebug... wait a second, Firebug?! had my wife taken on some web development projects recently? is she editing CSS style sheets in her spare time?

I took it out, and of course, everything now works smoothly. But now I'm curious - what would lead to the installation of Firebug, a highly specialized extension, for anyone who is not specifically in the field of web development? talk about a head-scratcher.