I found that this bug will also exist in situations when you use margin auto in CSS.
For example, in a fixed width & center aligned layout its typical to use "margin: 0px auto;" to keep a content well centered. This seems to produce possible (likely) decimal left/right margins for the content well. That isn't really a problem for Firefox.. it handles decimal pixel offsets just fine.
But Flash widgets totally seem to freak out when their object container are positioned with decimal pixel values. At minimum, you cannot interact with the "Allow" button. To me, this seems to be the root cause of this bug you will see widely reported by many (as it pertains to FF atleast).
As for why it only occurs in FF, I'm not entirely sure. On my OSX machine, Safari and Chrome don't exhibit this behavior with flash objects. Perhaps all DOM elements in Webkit are rendered with rounded pixel offset values automatically?
For Firefox, I implemented this workaround (useful for center aligned designs):
$(document).ready( function() {
repositionContentContainer();
});
function repositionContentContainer() {
// this routine is a complete hack to work around the flash "Allow" button bug
if ( $("#content").length > 0 ) {
//Adjust the #content left-margin, since by default it likely isn't an int
setLeftMargin();
//If the User resizes the window, adjust the #content left-margin
$(window).bind("resize", function() { setLeftMargin(); });
}
}
function setLeftMargin() {
var newWindowWidth = $(window).width();
var mainWellWidth = $("#content").width();
// create an integer based left_offset number
var left_offset = parseInt((newWindowWidth - mainWellWidth)/2.0);
if (left_offset < 0) { left_offset = 0; }
$("#content").css("margin-left", left_offset);
}