Have you updated your web browser lately? If the answer is “no” and you are running Firefox (or Firefox Quantum, as Mozilla calls it these days), there is a new build available, version 67.0. This is a finalized release and not a beta build, and it brings with it improved performance and some new features, including a cryptocurrency mining

Source: Hot Hardware – Firefox Quantum 67 Blazes Forward With Performance Boost And Cryptomining Blocker