In essence: It makes it random. (Hence fingerprinting checkers find the ID uniqiue")
Although sometimes you need some features that interfere with it. I use the add-on "Toggle Resist fingerprinting" to easily toggle it off when I want a website to draw canvas (canva.com is a funny example lol) and then toggle it back when I'm done.
Some nice things, but it can interfere with some daily use cases: Timezone is changed to UTC. Canvas shows random data.
Nice rabbit hole read: https://wiki.mozilla.org/Security/Fingerprinting
(Its like Wikipedia. You can't stop clicking on links to find out more xD)
EDIT: fingerprint.com probably use Cookies and/or localstorage so the ID is the same when refreshing, but Firefox have protection in place for cross-site tracking and cookie sandboxing, etc (I won’t pretend like I know how everything work), but those protections helps against that type of services from what I recall.
I finally made a Lemmy account just to comment on this 😅
When this option is active, of course your fingerprint is unique because of how it works.
Every time a website fingerprints you with this option turned on, firefox makes sure that the ID is as unique as possible, so no correlation can happen. 😊 Verify this by visiting that site two times and check the hash to make sure it change between the two requests.
EDIT: fingerprint.com probably use Cookies and/or localstorage so the ID is the same when refreshing, but Firefox have protection in place for cross-site tracking and cookie sandboxing, etc (I won’t pretend like I know how everything work), but those protections helps against that type of services from what I recall.