The forum seems to scale images up slightly in Firefox. I just noticed this when I changed my sig to include an image.
The text was fuzzy on this forum, so I compared the image on this forum to the image on another forum and it is not the same size.
I checked other images between IE and Firefox it seems that all images on this forum are slightly scaled up. Only Firefox seems to be doing this, but Firefox only has this issue on this forum.
System stats: Windows XP pro SP3, Firefox 3.6.3, IE 8.0.6001.
This shows the scaling of the Sig image in Firefox vs the actual image:
This is a stacked window arrangement:
Firefox 3.6.3 on another forum.
IE 8.0.6001 on this forum.
Firefox 3.6.3 on this forum.
Note the avatar image is also scaled, and so is "edit, quote, reply, report."