Apple introduced the viewport meta tag in mobile Safari to help web developers improve the presentation of there web pages on the iPhone. We added support for the viewport tag in mobile Firefox for the same reasons.
The viewport tag allows web developers to set the width, height and scale of the browser area used to display web content. However, some websites are not doing a good job configuring the viewport tag and it affects the presentation in Firefox.
When setting the width or height, developers can use a fixed number of pixels or use the constants: device-width and device-height. The iPhone is 320px wide in portrait and 480px wide in landscape. Other devices have different screen sizes. It seems the “width=320” is a popular fallback though. See how Facebook and DeviantART display in Firefox on the N900 (480px in portrait and 800px in landscape):
Don’t get me wrong. I like “touch-friendly” web pages on my mobile device. However, the iPhone is not the only mobile device out there. If a web developer has gone through the effort to make a “touch-friendly” web page, please configure your viewport to work in other devices. It’s easy!