is there a recovery system? I'd been working on a drawing for an obscene number of hours, when another tab decided to die...

If you saved/submitted your image, yes, otherwise, no. :-(
You should consider using a browser like Chrome that runs each tab in a separate process (so if one crashes, it doesn't bring down your whole browser). Also, save/take screenshots.

good call. luckily i have screenshots of the lines, so it might be workable in some other prog. thanks for the tip!