You can download an installer for Firefox 34.0.5 from the following page (scroll down to your preferred language): https://www.mozilla.org/firefox/all/ When you run the installer, it should detect your existing installation of Firefox 16 and update it. Have you already tried/failed that way? There have been a lot of changes, both under the hood and in the user interface, between Firefox 16 and Firefox 34. As part of the process, various files will need to be converted and while this usually works seamlessly, making very big leap of versions can cause glitches. Therefore, I suggest making a backup of your Firefox settings folder (profile folder) before running the update. This article has tips on that: [[Back up and restore information in Firefox profiles]].