My favorite Firefox extension, used dozens of times a day, is Zoom Image.

Want to see a photo on a Web page larger? Put your cursor on it, hold down the right mouse button and use the scroll wheel to reduce or enlarge it right in the page.

Or simply press the right button, then the left and the image enlarges to fit as much of the browser window as it can without cropping itself.

Photos will get vaguer as they get larger, but even so, most are still easier to read than the small versions chosen to let pages load quickly.

You'll see how handy this could be at the Guardian's six-photo slideshow from The Dawn of Colour: Centenary of the Autochrome at the National Media Museum. (How does it work? explains Autochrome.)

Check out The dryad, c. 1910. I wanted to see that dress, so I zoomed to fit, captured that part of the screen with MWSnap, saved and uploaded the photo at right.

You might also want to blow up a color photo of Mark Twain reading in bed.