Firefox is no longer supported on this version of Android.
If you have already installed Firefox, it will remain on your device until you uninstall it, but it will no longer be updated with new features or security and stability fixes.
For the best Firefox experience, see if a newer version of Android is available for your tablet or phone, to use the latest version of Firefox.
Get a supported version of Android
Check to see if a system update is available for your device. See Will Firefox work on my mobile device? for information on versions of Android that Firefox supports.
Update to the latest version of Firefox
Once you’ve updated to a supported version of Android, see this article on how to update to the latest version of Firefox for Android.