upgrade to Firefox 21

Conflicts:
	theme/chrome/browser/browser.css
	theme/chrome/browser/newtab/newTab.css
	theme/chrome/browser/tabview/tabview.css
	theme/chrome/global/findBar.css
	theme/chrome/mozapps/plugins/pluginProblem.css
New symbolic icon: identity-icons-https-mixed-active.svg
Fixed undo area on about:newtab
Merge branch 'upgrade-to-21'
Bumped up to version 21.1