When a bug is found, how dangerous is it? That’s the question because to not patch your system means you assume the risk that bug won’t be used to break in to your system. Both the Firefox and Tor browsers have been patched to close the underlying bug reported here yesterday.
The new version of Firefox is 50.0.2. One of my systems ran two updates in quick succession to get to 50.0.2. To check your current version and get the update if needed, run Firefox and look at Help | About Firefox. This dialog shows your current version and has a button to start the update process if needed. Do that and install the updated version immediately. The underlying bug existed in the Mac and Linux versions of Firefox so all unpatched systems are vulnerable.
Read the updated article on Ars Technica.