Quit Firefox Effectively

First make sure Firefox is not running:

ps ax | grep [f]irefox

If it is running, quit it. If it doesn't appear to be running but appears in the list from ps ax , kill it by running killall firefox , waiting a few seconds, then running killall -KILL firefox . If you don't see firefox: no process found after the second killall command, run that second command again. If you still don't see it, reboot (or you may want to try running it with sudo too, thought that won't usually help).

Consider Clearing Your Profile

If you want to clear out your profile (which can fix many problems, especially problems relating to upgrading Firefox to a new version), then rename the folder called .mozilla that resides in your home folder. There's two ways to do this:

In Nautilus (the GUI file browser): Press Ctrl + H or click View → Show Hidden Files . Then you can see files and folders that start with a . . Go to your home folder if you're not already there, and rename .mozilla to .mozilla.old (or whatever you want to call it).

On the command-line: Open a Terminal window ( Ctrl + Alt + T ) and run the command: mv ~/.mozilla ~/.mozilla.old (Or put whatever you want to call it, in place of .mozilla.old .)

The idea behind renaming the folder instead of deleting it is so you can restore it. But if its contents are keeping Firefox (or a recently installed newer version of Firefox) from working, then you may have trouble actually using them later!

Therefore, if there's anything you want to save--often, this will be your bookmarks--you should back that up first, before you do this. (This article may help with that.)

Finally, note that I'm certainly not advocating clearing your profile regularly, or even every time you upgrade Firefox. It's only when you have severe problems after upgrading that I recommend trying it. (If it makes no difference, you can rename .mozilla.old back to .mozilla --you may have to remove a newly created .mozilla first. That's one of the reasons to back up the whole profile.)

Reinstall Firefox (from the latest version in any of your software sources)

To reinstall Firefox, removing global configuration files and getting the latest version available in any of the software sources configured on your Ubuntu system, run:

sudo apt-get update sudo apt-get --purge --reinstall install firefox

Should apt-get upgrade be run too?

Running sudo apt-get upgrade is not necessary for getting the latest available Firefox, because the install command will automatically fetch and install or upgrade to the latest installable version, and whatever other packages (if any) are needed to enable that version to install.

With that said, it's reasonable to run sudo apt-get upgrade in this situation. You may want to bring all your software up to date, and that can even potentially help with some interoperability problems. (New versions of some packages and really old versions of others have not necessarily been tested together, after all.)

If you're accustomed to using the Software Updater (Update Manager in older Ubuntu releases), go ahead and do that. If you prefer to use the command-line:

sudo apt-get upgrade sudo apt-get dist-upgrade

Of course, if you haven't run sudo apt-get update shortly before running those, you should do that. And sudo apt-get dist-upgrade will upgrade packages that require the installation of new packages or removal of currently installed packages, so you should make sure to look at what it says it plans to do, before letting it proceed.