Class names are considered case sensitive in HTML, and CSS selectors honor this except when in quirks mode. I suspect you're activating quirks mode when you mes

Class names are considered case sensitive in HTML, and CSS selectors honor this except when in quirks mode. I suspect you're activating quirks mode when you mess with the doctype, causing the matching behavior to become case insensitive. This should be the same in Firefox as well, but I haven't tested it.