Mouse wheel now ‘scrolls’ page forward/back function. WTF?

About five minutes ago it started.

Acer Aspire 1363 WLMi, 2GB, nVidia GeForce 5200 128MB, Acrox 800 dpi 5-button mouse
The mouse scroll wheel won’t scroll through anything – it acts like the browser page back, page forward function – the function that the left and right mouse buttons have done for years.

I’m currently relegated to using screen border scrollers and Firefox drop-menu arrows.

It is really getting on my T!TS !!!

Any ideas how to get my normal scroller back?