If you use Firefox, whether on a Windows device, Mac or Linux, you need to upgrade it to version 39.0.3 because of a security vulnerability in all previous versions.

If you use Firefox with FTP clients, Subversion, or any other software that uses saved passwords, you should change the stored passwords.

If you have SSH keys saved, which allow SSH login to servers without entering passwords, delete them and replace them immediately (both on your local machine and the server they are connecting to).

Full story:
http://blogs.kent.ac.uk/isnews/if-you-use-firefox-update-it-today/