Differences in geolocation accuracy between browsers

I am trying to understand why, when I use geolocation with different browsers on the same computer, I have different results. I know that the implementation of this function is not perfect ... but, this is strange, because I try on a computer with chrome and FF4.1, and I got good accuracy. On the same computer, IE gives me poor accuracy. When I try to use another computer with chrome and FF 4.1, Chrome gives me a good result, and firefox gives me the same poor accuracy as IE (ip location, I think).

If someone has a solution to get the same accuracy for the entire browser, or just for an explanation?