Upgrading Firefox Portable
To upgrade to a newer version of Firefox Portable, just install a new copy of Firefox Portable right over your old one. All your data will be preserved. At this time, please don't use the auto-updater due to a bug. More information here.
If you're upgrading from Portable Firefox (older name and directories), make a copy of your existing profile folder within the PortableFirefox\Data\profile directory on your portable drive. Then download the new version of Firefox Portable and copy your profile from the old version into the new version within FirefoxPortable\Data\profile. If you added any plugins or searchplugins, you should copy those directories as well (PortableFirefox\plugins to FirefoxPortable\Data\plugins and PortableFirefox\firefox\searchplugins to FirefoxPortable\App\firefox\searchplugins).