Disable your referrer header by default
In HTTP, there exists a header caller Referer, which contains information about which site you are coming from when following a link 1.
It can contain a partial, or complete URL.
Obviously, this has privacy implications.
This is why in much self-hosted software for instance, you will see the Referrer-Policy header being set to no-referrer 2.
In Firefox, the default behaviour is to transmit referrer information.
If you don’t want this behaviour, there exists the option network.http.referer.defaultPolicy in about:config.
For a couple of weeks I have set it to 0, and it has given me almost no problems.
Turns out, if a website cares about your referrer, they will explicitly state what they expect in a header or in the <head> 3.
Therefore, I whole-heartedly recommend setting this header.
For more information, see the Firefox documentation.