Sometimes resistFingerprinting can break some site, but rarely. But if it happens the addon "Toggle Resist Fingerprinting" [1] can be helpful to temporarily inactivate it with a simple click on an button. Instead of having to go to about:config and change "privacy.resistFingerprinting" to "false" manually.
[1] https://addons.mozilla.org/en-US/firefox/addon/toggle-resist...