Please explain what the proper behavior of getSelection on a display:none iframe is
Sorry for the long time to respond -- I was on vacation for a while, then spent a while doing other things.
The editing spec says "Every browsing context has a selection." <http://dvcs.w3.org/hg/editing/raw-file/tip/editing.html#selections> The HTML spec says "When an iframe element is first inserted into a document, the user agent must create a nested browsing context". <http://www.whatwg.org/specs/web-apps/current-work/multipage/the-iframe-element.html#the-iframe-element> Thus the spec implies that any iframe in a document has a selection. Testing, this is how IE9, Chrome 17 dev, and Opera Next 12.00 alpha behave. Firefox 12.0a1 returns null from getSelection() if the iframe is display: none. I don't see any advantage to Gecko's behavior, so I'll stick with the behavior of the majority of browsers -- display: none should make no difference.
Reopen if you don't think the spec is clear enough.