Upgrade to Firefox 28.0 beta 2

Conflicts:
	theme/chrome/browser/browser.css
	theme/chrome/browser/devtools/toolbox.css
	theme/chrome/global/findBar.css
Return support Firefox 27
Add [forwardshowalways] attribute (for Tweaks extension)
Add box-shadow for toobarbuttons in :hover state
Merge branch 'upgrade-to-28'