Web-based image editor Picnik, which is , has long been the photo-hosting service. And if you've found yourself wishing it was just as simple to edit other images around the Web, you're in luck. A relatively new Firefox extension called "Instant Image Edit with Picnik" lets you edit any image on any site, using Picnik--all with little more than a right-click.
The extension was built using a new part of Mozilla's Jetpack API, which lets developers add items to the contextual menu of a user's browser. In this case it's a link to "edit image with Picnik," which shows up when you right-click on an image. Doing so kicks you out to Picnik's Adobe Flash-based editor, which will load up the image editor in a new tab without you even having to sign in or register for Picnik itself.
There is one big caveat, which is more an issue with the way Picnik acquires the images than what the extension does. Picnik cannot fetch images that are behind a VPN or password-protected page. This means you can't go and edit a photo you've received in your Web mail in-box without first downloading it locally, or hosting it elsewhere. That aside, with this installed you can get the same kind of Flickr-like simplicity for editing your photos in places like Picasa and Facebook--all without having to head over to Picnik to get things started.
Chrome users should not feel too left out, as there's a similar extension (and a first-party one at that) from Picnik that lets you do the same thing.