Yes, the exact same thing happened to me! Took me awhile to figure it out because I'm setting up a new install of ZenCart and I didn't know if all the data imported badly or what was happening.

I do have the latest version of PHP, installed yesterday. So that's not it.

You said, "Mozilla" ... and I use Chrome. So I dropped Chrome and used IE-9 instead. With IE-9, the product editor works fine.

It's a relief to know what's causing it. I hate to give up Chrome but it's been doing some weird things lately. Chrome doesn't approve of my secure certificate either, but IE does.

(I know the smileys are childish, but you've got some I haven't seen.)

Cyndy