Content in the Facebook search bar is automatically filled/completed by Facebook, not Firefox.

Same happens at other websites too

The same information applies to other sites as well. It's the website that's offering that search suggestion, not Firefox.

Such suggestions are provided via JavaScript and a script sends why you have typed so far to the server as an XHR request. You can confirm this by checking the Network Monitor and filter by XHR.

• https://developer.mozilla.org/en-US/Tools/Network_Monitor