Most of the srilankan are facing this problem ,,,,,,,, Here is the solution
If you want to see sinhala fonts face book Fb or what ever you have to download Sihala unicode
then you want restart your browser you can see sinhala fonts.............
If you want to write sinhala fonts in facebook (sinhala fonts) you have to download that perticular software(sinhala Unicode)
Then you go to start bar you can see as pic shows you click and change to sinhala......... you can write sinhala fonts in facebook