Screen tearing in firefox is resolved by enabling hardware acceleration in firefox. It's disabled by default as it causes issues in some setups. Firefox was last updated March 24th and it did not change this default setting.
You can read about it and other solutions such as enabling Force Full Composition Pipeline in nvidia-settings here : https://discuss.getsol.us/d/146-linux-survival-guide should you find the problem hasn't been solved by Celtic magic. 😛
