What browser extension you couldn't live without?

So, recently I've stumbled upon an extension that made me a lot more productive and maybe it will help some of you too.
The extension is Vimium
What it does: help you navigate websites without using your mouse or touchpad.

Get it:

• https://chrome.google.com/webstore/detail/vimium/dbepggeogbaibhgnhhndojpepiihcmeb?hl=en
• https://addons.mozilla.org/en-US/firefox/addon/vimium-ff/

To see all the shortcuts available you can just press '?'.

So what browser extension is making your more productive?

PS: I've navigated IH website to make this post using the extension. :)