jQuery Forum

As of iOS 5.0 (I'd been testing against 4.3 and 4.2), both fixed background-attachment, as well as fixed position on other elements works consistently with compliant desktop browsers; however, before this, pretty much no mobile browser correctly implemented fixed positioning.  The reason is mobile browsers were begun as really desktop-lite browsers that would, for the sake of especially zooming (but of course therefore scrolling), essentially take a snapshot of the webpage and then let the browser's viewport be manipulated as a static image.  This of course means that those elements that are fixed to the bottom of the page, or to fill the background of the page, actually only snapped to the bottom of or filled that initial, top-scrolled, rendering of the page, and when the page is scrolled, all those fixed elements are actually fixed to the first rendering of the page, and essentially totally un-fixed.  As I said, iOS 5.x already correctly supports fixed.  However, I can't say the same of other mobile browsers - even WebKit-based browsers such as those in Android devices.