Strange Image Problem with Firefox

I've run into this a few times so far when installing and testing out the WebsiteBaker script, it seems if an image is of a certain dimension/proportion, and you insert it into the page, it becomes invisible in Firefox. There were two JPEG images I had that were about 400px x 630px (roughly, I dont recall the exact numbers), 72DPI. Every time I inserted them into a page, they would display in IE, but not in Firefox. When I loaded the admin section up in firefox, and went to edit the page, they wouldn't appear there either. If I looked at the source code of the page, an inline CSS tag of "display:none" was being tacked on to the Image HTML for some reason.

If I took the images, and resized them a bit to a different proportion, like 400 x 600 instead, they would display just fine on the page. I even tried switching from FCKEditor to Xinha and had the same problem. Would this possibly have something to do with UTF/Unicode or something?

I did use the "display:none" property once within the style sheet. I had all the H1 tags set to it, because I was using a graphic for the logo instead. However I checked and the image HTML was not contained anywhere within the H1 tags on any of the pages.