Change your update preference from automatic to notification. See this article:

https://support.mozilla.org/en-US/kb/update-firefox-latest-version#w_how-do-i-configure-update-32optionssf33preferencessf

By the way, after each update Mozilla publishes the security vulnerabilities in the previous release, so running old versions does expose you to potential exploits. I have no idea why you can't run Firefox 14 on your version of Facebook (???), but you will have to decide what level of risk to run. Good system backups are advisable.

Options-Advanced-Updates-Select check for updates but let me choose to install, you may be able to get some security updates but as mentioned above your PC will be at risk somewhat. Keep your Microsoft Security up to date and run a good adaware program daily there are many great ones I love CC-Cleaner it's listed highly ranked with C-Net I've had my PC for 10 years (with several upgrades lol I'm attached) But between Microsoft Security and CC-Cleaner I've never crashed or had a virus, Use Facebook regularly however I do run CC-Cleaner every time before I log off it only takes a few seconds. I would uninstall the Firefox 14 and download a fresh copy of the version you want. I run Firefox UX nightly and it runs with Facebook extremely well plus you get more add ons and security. Whatever you decide to reinstall the steps in the beginning are the same for changing update behavior. Good luck Rhondar35

problem solved thak you