Then I would really check what other apps might be interfering. You may want to try shutting down all other apps that you have installed (not standard ones, but ones you yourself downloaded) and see if that allows it to work.
If not, you may wind up having to save all your personal stuff (photos, videos, music, contacts, etc.,) to a computer or cloud account and then do a hard reset of the tablet. Once it is done, then install that app only (if didn't come on the tablet) and don't install any other new apps. See if it works OK. If it does. Then try installing apps one at a time, and then seeing if the problem shows up. Eventually you will run into the app that is the cause (if it is an app that is).
Otherwise I would contact facebook and ask them about it.
NOTE: Doing this will clear 'all' the data on your tablet, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the device.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the tablet...
1. Make sure that the tablet is actually powered off.
2. Remove your SD card, if there is one in the device.
3. Press the "Power" and the "Volume Up" buttons, together, until you see the start-up logo on the screen.
4. Once you can see the logo, release the buttons and allow the device to enter the "System Recovery Mode".
5. Next use "Volume Down" button to get to the "wipe data/factory reset" option When in recovery mode the "Volume Up" and "Volume Down" buttons are how to can navigate and highlight what option you need.
6. Once you have selected the "wipe data/factory reset", press the "Power" button to select that option.
7. On the following screen, repeatedly press the "Volume Down" button until the "Yes - delete all user data" option is what is selected.
8. Then press the "Power" button to hard reset the tablet.
9. If you took your SD card out in step 2, when the device is up and running again, reinsert the SD card.