Pretty good, but when I'm using a dark theme for Firefox the addon's text appears as black-on-dark-grey.

Great stuff! Only thing that sucks is that (at least for me) I can't save images on tumblr. "image failed to load. this image cannot be saved." is the message that shows up when I try. So far I've only seen this error pop up on that website. I also tried the extension on Chrome, same result.
I'd love it if this got fixed.