My Firefox 3.0.4 does not display non-existing images at all, or it displays the image alt as plain text (if available).
This way I would have no idea that there is supposed to be an image there.
Does anyone know if there is a way to make it work like IE/Opera? (ie. display a box even if the image file doesn't exists) - plugin or anything?
Thanks in advance!
As far as i know there is no plugin, Images should have a width and height specified like so:
<img src='...' width='100' height='100' alt='...'></img>
or
<img src='...' alt='...' style='width:100px; height:100px;'></img>
Then firefox will reserve the appropiate space for the images.
You could get the Firebug Plugin. It won't change how the images show up, but it does have a network tab that you can click to see which resources were gotten by firefox (and how fast). As well, it will tell you what images, js files and css files it was not able to get. It's incredibly handy for web development.
It also has a ton of other great features like JS debugging, and so much more.
There's an experimental Force Image Placeholders plugin which attempts to do what you request. I haven't used it, but it's worth a try.
Along the lines of Pim Jager's suggestion, but it seems as though you'll need to force the image to display with something like "display: block;". This has the advantage of allowing you to specify additional styles via CSS that will show if the image doesn't - e.g. a background-color, or even a background-image. YMMV.
Upon further reflection, there is a problem with setting the background color/image. The background will show through any transparency in the images.