Open a command prompt and execute the appropriate command for your distribution:
sudo apt-get update && sudo apt-get dist-upgrade
sudo dnf update --refresh
sudo yum update
sudo pacman -Syu
sudo zypper dup
Note: Some apps require new permissions when they are updated. You may see a notification asking if you accept the new permissions.
You could drive around with old, burned-out brake lights on your car, but it would make driving more dangerous than it should be. And if we all did that, it would get really dangerous, fast! Letting your system get out of date can encourage malicious actors online, which makes everyone vulnerable.
Mozilla cares about your privacy and security everywhere, not just on Firefox. The safer the Internet is, the easier it is to create and keep it open. So please take a minute to update your software. The Web will thank you.