For animated GIFs, I've always used an online GIF maker. These online tools tend to be extremely simple and easy to use, so most of the time I will use these simple tools to manipulate animated GIFs instead of Photoshop, which seems to require a level of complexity for even simple tasks.
This time the issue was that I needed to crop an animated GIF because it was showing a prescription bottle in the background with highly personal information on it. And it dawned on me that I didn't know how to crop a GIF that had already been animated with multiple frames. A couple times I've cropped the frames separately but that's a huge hassle, and I figured there had to be a better way.
It drove me crazy figuring this out, and here's what I did:
1. When you open an animated GIF, Photoshop CS6 shows you all the layers on the side, but you only need to crop just one layer--whatever layer it happens to land you on is fine. When you go to Image -> Crop then it will crop all layers. Originally I had done Select -> All Layers but that turned out to be unnecessary, and I went back and tested it again. So all you need to do is crop one of the layers, and you will see all the layers on the side bar change size.
2. Now go to File -> Save for Web and you will get a window giving you access to all the settings for the GIF you're about to save. Then press the OK button, choose a file name and you're all set.