I've now got myibidder successfully installed on Firefox and see how I can add a snipe. But how do I cancel the snipe if I change my mind? (I expect there will be a screen that comes up allowing me to cancel, but I just want to be sure before committing to bidding on something.)

You can login to https://www.myibidder.com/ to manage all your snipes. You can also remove your snipe, change your snipe and de-activate every snipe there.

OK, thanks!