1. HTTPS Everywhere – This extension will force secure SSL connection between your browser and a website (where possible). Created by the Electronic Frontier Foundation.
  2. Disconnect.me – A plugin which will show you who are tracking you at the exact moment.
  3. EditThisCookie – If you know what are cookies in your browser and what they do, then this extension will allow you to edit them in bulk or individually.
  4. AdBlock Plus – Not only removes ads from websites, but it can also prevent advertising networks from collection informations about you (through the ads).
  5. NoScript – This plugin disables JavaScript, making harder for websites to collect information. ScriptSafe is a Chrome alternative, since NoScript is Firefox only.
  6. Blur – Formerly known as Do Not Track Me. Blur will let you decide who what information can collect about you. Also several other awesome tools are ready for use in this useful extension, like email masker.
  7. LastPass – A password manager extension. This extension will create different passwords (strong ones) for different websites and you will have to only remember your master password.
  8. RequestPolicy – Extension that gives you control over cross-site requests. Open source, but available for Firefox only.
  9. Web of Trust – Gives you information about which site should you trust and which not.
  10. Ghostery – This useful plugin will give you the control to decide which cookies and scripts can run by default.