hey android's users! had u ever met this kind of annoying downloading status on your status bar?
well... here is the solution:
1) download the app called "app drawer" via play store
2) run the app
3) scroll to the item named "downloads"
4) look for the word "facebook". if it's not available on the 1st tab, click on the 2nd tab.
5) when u found it. tick the checkbox and click on the dustbin's icon to delete it.
6) voila! it's gone!