The obvious questions: does Google work with the OTHER browser? (Internet Explorer), or updating to Firefox 3.5.2

A longshot: Power down everything for 10 seconds. Modem. Router. Cut power to Computer.

Note that on desktop computer, you MUST switch off the power switch at the back on the power supply (or switch off the power bar). I once had wonky internet performance for months until I realized that (like some USB ports) the internet port on my computer remained powered up even when the computer was apparently shut down (using Windows -> shut down) (this is to allow computers to be turned on remotely over a network). The wonkiness of my connection showed up on certain sites, but not other, less-complicated sites. Everything would slow to a crawl until I rebooted. However, once the internet port was actually powered off, it came up again in a much more stable manner.