Is there a way to block on a certain site on your web browser?

[raginranger]

Just curious if this is possible. I almost need to block amazon to keep me from spending too much money. I use firefox btw. Does anyone know of a way to do this? I suppose I could always "unblock" it, but I think if it's blocked initially it would at least serve as a deterrent to keep me in check.

thanks in advance.