It has become common to view and add Emoji 😝😈😬 to emails, tweets, blogposts or any text on the web.
Emoji Cheatsheet (also known as Emoji Helper) is a fantastic extension for Firefox that is an emoji picker. It helps to pick emoji from a gallery and insert into any text input or copy to clipboard. The emoji you picked can be inserted as Unicode character, as text code (like that used in Github) or an image (for old applications). Almost all the emoji you see available on your smartphone seems to be in its collection.
Emoji Cheatsheet can be installed from here.
Check the extension preferences for picking your preferred mode (Unicode, text code or image), keyboard shortcut and other goodies!
Tried with: Emoji Cheatsheet 1.1.1, Firefox 41.0 and Ubuntu 14.04