How to remove User-Agent for Firefox

There is a way to do this without any addons:

• enter "about:config" into the URL bar. Press Enter.
• create a new entry with key=general.useragent.override and an empty string as a value.
• If you use an old version of Firefox, you also need to set the key general.useragent.enable_overrides to true.

This way your browrer will not send any "User Agent" at all. You can check this by doing:

• open firefox network view with Ctrl Shift Q
• load any URL you want
• click on a web request and see the "Request Headers" on the right. There should be no "User-Agent" entry if you've done it right.

P.S. Your browser may still be leaked if you have JS enabled for a site. This is because each browser has its own rendering capabilities, supported formats etc. The described steps remove "User-Agent" request headers, that's all.