Wow, this must be the most convenient add-on that you could find for reverse image searching.
BUT, like other add-ons, it does not support searching private images (in which case it should download the image first then post it to search engines).
Edit (reply to author): I just noticed that actually I could copy the image to clipboard and then paste to the "Upload" page. Not that convenient but it works :) Ideally it would be nice to have a server to test whether an image is publicly available before performing queries but sounds like an overkill? Anyway, awesome job, thanks!