It's isn't the default because the countermeasures cause a lot of side-effects. If it were on by default, new users would probably think the browser is broken o

It's isn't the default because the countermeasures cause a lot of side-effects. If it were on by default, new users would probably think the browser is broken or buggy. Here's what the settings do and what sort of side-effects you might experience: https://support.mozilla.org/en-US/kb/resist-fingerprinting https://support.mozilla.org/en-US/kb/resist-fingerprinting