Similar to Google Chrome and other known browsers there are thousands of Add-ons available for Mozilla Firefox too. You can find them in Menu>Add-ons quickly. There are some websites which provide extensions for Firefox browser, but their add-ons are not listed in the store of Firefox browser. Such type of extensions is called unsigned.
Earlier, people could easily install any add-ons whether it's signed or unsigned but after the update 43, it got disabled by the company. From version 43, one could no longer install them. You will get a security warning saying "Firefox has prevented this site from installing an unverified add-on" whenever you try to install them in your browser.
Still, if you are willing to install an extension not listed in the Firefox gallery then here's a trick which will let you install any unsigned add-ones. You just need to bypass this security notification, and you're done.
Note: - Use this method only in the case if you're confirmed about the safety of the extension.
How to Install Unverified Add-ons in Firefox
- Enter about: config in your address bar and hit enter.
- You might come across a security warning saying This might void your warranty!
- Ignore it, just tap I'll be careful, I promise!
- On the next page, you can notice all the settings to customize Firefox.
- Now enter xpinstall.signatures.required (enter the exact text as it's case sensitive) in the search bar. It will automatically search for the particular setting.
- Notice the Value tab; it should be True by default.
- Double click on the setting to set it False. That's it.
- Now you can get Install button for unverified add-ons too.