Q:

Firefox 8.0 doesn't resize content like other browsers

I'm making a page to scale down to fairly small browser sizes, including on desktops.  I've got it down for pretty much every browser but firefox; it just doesn't make the content smaller the same way as other browsers.
Say I have a simple page like this:
<body>
    <div style="width:auto; max-width:500px; margin:20px;background-color:black;"> Some filler text </div>
</body>

If you try that in any browser but firefox, when you resize the window to smaller than 540px, the div gets smaller, as you would expect.  But in firefox, it does no such thing. At least not in 8.0.  It resizes the div a tiny amount and then lets it extend off the window, without even leaving a scrollbar.   
Is there any way around this behavior?
EDIT:  I've reproduced this is on older versions of firefox as well, but I found something odd.  When I said it resizes the div a tiny amount, here's what happens: the body of the page stays at 367px width.  Two different versions of firefox, two versions of windows, the same number.

A:

The issue you're running into is that in Firefox depending on the exact themes or extensions in use as you resize the browser window the browser content area may not resize (because, for example, the various buttons on the widest toolbar impose a minimum width on that content area due to the way the user interface is laid out).
This is why you see the body not changing size: the CSS viewport itself is not changing size.  If your page had a vertical scrollbar, you'd see that scrollbar disappear off the right edge of the window, just like parts of the browser UI itself disappear.
You can work around this with enough toolbar customization (e.g. remove everything from the toolbars) if you just need this for testing.  On the other hand if you just need this for testing you can probably jut load the site in an iframe which you then size however you want...

