Things to check

• Log in/ Log out
• Registration/ Password reset
• Homepage-> Browse Add-ons(check for sorts)
• Category landing/browse pages
• Search for:
  • extension
  • persona
  • collection
  • super-popular stuff like "Firebug", "Adblock-plus", "twitter" etc
• Add a review
• Install extension(public/lite) from AMO
• Install a search tool(.xml)
• Install a public extension from API[4.0/3.6]
• Search for an extension in API(Firefox, Thunderbird,Mobile)[4.0/3.6]
• Featured add-ons
• Download a non-FF extension(thunderbird or mobile)
• Footer links
• Load collections landing page
• Create a collection
• All versions page
• Unreviewed add-ons are not on homepage, API or any other pages, where they are not welcome.
• SRC attributes
• Discovery Pane

Other items

• Run the Link Validator