As of the official implementation of Gecko version 1.9.2, there will be a tag implemented that chooses the resizing algorithm used on a page, allowing you to choose between Nearest Neighbor (direct resize, no blur), Bilinear Filtering (low quality blur, which is currently used), or Bicubic Blur (high quality blur, what photoshop uses). Meaning that we'll no longer have blurry pixel art when we resize.

https://developer.mozilla.org/En/CSS/image-rendering

This is the official documentation. It'll be stuck in along with HTML 5, meaning that you can probably try out the new tags in the current Firefox 3.5 beta.

The tags to be added into the CSS styles are as follows:

img[src$=".gif"] { image-rendering: -moz-crisp-edges; -ms-interpolation-mode: nearest-neighbor; }
img[src$=".png"] { image-rendering: -moz-crisp-edges; -ms-interpolation-mode: nearest-neighbor; }

For an invidual image you'd use this code (can be factored into the  BBcodes in the forum, and the display for individual images on the site):

<img style="-ms-interpolation-mode:nearest-neighbor" alt="images/WhateverAlt.jpg" src="images/Whatever.jpg"/>

The code will be fully implemented in Firefox 3.5, but as mentioned above, you can try it out now in the beta version.