Are you running Firefox version 67.0.3 or Firefox ESR 60.7.1? If the answer is "no" or you're not sure, maybe just update your web browser now. The Firefox maker Mozilla warns (through ZDNet ) that the browser has a zero-day fault that is being exploited actively in nature (you do not see that every day) and has issued a patch of emergency that can allow you to plug that hole right now.
Here is the full description of the problem:
Updating Firefox can be as easy as restarting the browser, although you can also touch the hamburger icon in the upper right corner, type "Update" in the search and hit the "Restart to update Firefox" button to be sure. Or simply download a new copy here.
Either way, you're likely to see a "Congratulations! You're using the latest version of Firefox." Once you start the browser again.
It is not clear exactly what hackers are trying to obtain by actively exploiting this flaw, but stealing the cryptocurrency is a conjecture: the error was credited to Samuel Groß in his roles as a member of the security research division Project Zero of Google and the security team of Coinbase.