Pearl Crescent Page Saver
Mac and Windows only at this time. Linux support is planned for January 2006.
Pearl Crescent Page Saver is a free extension for Mozilla Firefox that lets you save an image of a web page to a file in PNG format. Options let you control whether images are saved at full size or scaled down to a smaller size (by default, images are saved at 25% of the original page size). The Page Saver extension uses the new canvas feature that was introduced in Firefox 1.5.