Ubuntu :: Internet Lags Then Goes To OpenDNS?

Anyway, my internet has been working fine until recently (last week or so). For most sites, Firefox will load the page quickly. However, every once in a while, but frequently enough to annoying, it will say "loading" for 10 seconds, then direct me to OpenDNS, which says the page cannot load. When I try it again, I get the same problem. Other sites are fine.

Then, when I quit Firefox and restart it, that site will work fine, but soon enough, another site stops loading properly.

For example, Google will work fine for awhile, then I'll get the error, but after restarting, Google will be fine again, but now Wikipedia, which loaded before, gets the error. And the cycle continues on yet another website...

I haven't changed any Internet or network settings recently. I'm on Ubuntu 10.04.