Firefox Issue

I like Firefox. I like it up until the point where it gives me the error shown in the attached picture. It has a Google logo and says it cannot find the page I’m looking for.

If I hit Refresh it says the same thing but if I double-click Refresh (which I did out of frustration one time) it will go to the page and work fine for a while.

I never have this problem when I’m using a different browser, which I’m usually forced to do because of the error.

My brother uses Firefox. When he’s home he experiences the same issue on his laptop but when’s he’s at school he never has the problem occur. The only difference is that we use a proxy here at home.

So have any of you had this happen or do you have any suggestions?