Wow. Yep, anything trying to add a watermark is broken in recent versions of Chrome. It's because the custom watermark URL field specifies that it's a URL, as a help for mobile editing; desktop Chrome has recently decided to start erroring if a field that says it should be a URL contains something that isn't one, even if that field is invisible... Gah.

Thanks for the report - I'll get this fixed ASAP. (Not quite sure how S that'll be, but it'll be ASAP.)

It happens in latest Opera as well as Opera Next (which claims to be Opera but is actually Chrome).

Halian: Thanks for reminding me to disable Opera's updates. (It took them YEARS to fix everything they broke moving to 6, and now they're just throwing their whole product away? Madness.)

Alex: Default to about:blank maybe? (And strip that out so it doesn't fill the db pointlessly?)

It's fine if you don't specify a watermark - "" is accepted. But selecting the "white mana" watermark populates the hidden URL field with "{White Mana}" (which the server then translates into the right image URL); and recent browsers have started complaining at the hidden URL field containing "{White Mana}".

As a workaround, you could use the hard-coded image URLs, http://multiverse.heroku.com/images/watermarks/w.png (u.png, b.png, r.png, g.png). Although those images will be moving when I roll out the next update (that'll be at least a few days away, though). Or you could just go without the watermarks for the moment until I roll out the fix in the next update.