The old FF came up because you launched it from (I suspect) the menu.
Anytime you edit program files, make certain the application's *closed.
Again, I suspect a menu launch..
Since my method works well for testing, storing the extracted pkg somewhere in /mnt/home is fine. With this setup you simply drag the binary to your desktop and avoid any menu launchers. Doing so would make the old build use components in the new FF settings folder. This you wanna avoid.Also had to rename /usr/lib/firefox-17.0.11 to /usr/lib/firefox-17.0.11_old.
The good thing is, if any part of your setup became *polluted,* and you weren't happy with the new build, you could always drop back to a smaller, less bloated, earlier version.
And Pup doesn't need any (firefox-17.0.11) numbered naming convention.. It's downright silly.
PS >> If you run NoScript, make sure'n backup your white list.