Why would anyone want to throttle the bandwidth of Firefox or Internet Explorer ? That was my first thought when I read about two tiny apps for Firefox and Internet Explorer for the first time at Sizlopedia. I mean, it is normally the other way round. You download some large file or use P2P networks and want to use a browser as well which means that there should be a way to assign a minimum amount of bandwidth for the browser instead of throttling it. Everyone should be capable of not download large files or browsing all those rich entertainment websites if he really needs the bandwidth for something else.
Internet Speed Simulator
Speed Simulator is a nice free tool that makes it possible to see how a website behaves under certain speed limitations. This is for instance useful if you want to see how a user with a 56K modem experiences your site and especially the loading time of it. Only the download speed can be reduced to simulate slower connections.

