I've never seen anything like this in 20 years of using Photoshop, so I'm not holding out much hope for an answer, but you never know...
This problem happens when I am using a brush and try to select a foreground color by clicking on the "Set Foreground Color" in the toolbox. The "Color Picker" appears, I choose a color, click "OK," and then a never-ending number of Firefox windows begins to open with the Photoshop help page (as if I repeatedly pressed the F1 key extremely quickly). I have to Ctrl-Alt-Del and quit Firefox or the opening of windows won't stop.
This doesn't happen every time I use the color picker to select a foreground color, but whenever it happens, that's what I'm doing.
I'm using Windows XP Pro x64 with 6GB RAM, Photoshop CS4, and a Wacom PTZ-631W tablet.
P.S. It has nothing to do with the Wacom tablet because I just found out that it's happening to another person in the department and he doesn't have a tablet. Also, I just found out that this has been happeining for about 5 years, before we upgraded to 64-bit XP Pro and before CS4. Now I'm wondering if the company has some sort of keystroke tracker that's interfering.
It's happened to almost every Photoshop user in almost every Photoshop version, and unfortunately to this day no one knows why.
There's a big thread on it over at the Photoshop error report / feature request site:
Can you reproduce it on demand? Adobe might be interested in that.
If you're just looking to get it fixed, some people have reported that updating display drivers helps.