A while back I wrote a post about removing the 3 pixel gap in Hotmail. While that provided a solution for IE I've since discovered another fix that works in Firefox. It's the same problem as before; a 3 pixel gap is added beneath images, particular to images inside table cells. The problem seems to stem from the font size settings, obviously this shouldn't affect a table cell that does not contain text. Chalk it up to yet another That Shouldn't Make Any Difference But It Does™ This time the fix is to add style="line-height: 50%" to the TD tag. You should then end up with the following:

Hotmail has a bug where a gap of 3 pixels appears in between images, even when the IMG tags have no spaces separating them. To fix this annoyance I've found that adding style="display: block;" to the IMG tag fixes this. I apply the fix as an inline style to avoid the CSS filtering of web based email services.

You should end up with the following for images that need the 3 pixel gap removing: