Cannot Crop Images

I’m not able to crop images in 3.5 — or at least I’m having lots of trouble figuring out how to do it. The instructions are the same as they’ve always been — click on the image, drag to select the desired part, etc. — but all it does is have a copy of the image moving with that universal zero-with-a-cross-thru-it symbol. I’m using Firefox. Also I have two blogs with separate themes, and it’s the same with both. Appreciate any help.