I agree to "ignore" Firefox on this one, since most users use IE anyway. I suspect we are talking of use in comercial websites or a commercial CMS anyway, which really makes it important to work in IE.
Sure - I use Firefox myself, but out customers don't, so we need IE.
This sollution doesnt sound very complicated when thinking of it, though in practise it might be much more complicated - sure. Firstly i would think that this system would need some sort of kerning, so that we can compensate for different font types and different font sizes in some way. Most likely we will be using Verdana or Arial - so the functionality could (doesnt have to) be made with this in mind, making some rules makes the goal easier to acomplish.
I would think that if we are talking of 12px size in text and verdana we could quickly determine how many characters in general that fits on say 5 lines of 120px width. Doing a 5 line calculation narrows the kerning and linebreaking that might occur on some words. But the main problem is as mentioned with the images.
I would think that we need to parse the entire text and pick out all the images so that we can modify them. We must deside that if content are split into 120px coloumns, an image can or cant be larger than 120px. if larger then we need to resize it and remove possible align. If we want align we must be sure that the image is small enough to have a practical use in the text, meaning probably resizing it down to max 50px in with or something.
Surely this can be solved, but doing all theese calculations in javascript Im not sure off - to me it sounds much better doing this serverside before pushing the content to the browser.
But it sounds like a good idea however, now I gotta run to purchase some christmas gifts,
regards,
Kim Steinhaug