Problem solved.
Pull the network cable from router to the notebook before browse to fb 😞
Cause of problem should be from server switching between 5.edge-chat.facebook.com and 6.edge-chat.facebook.com. Donno what inside the packets that disrupted wifi connection. With network cable connection, once I reach the end of the page and press PgDn, the opera's status bar showed that it was connecting to that edge-chat, hesitated for a few seconds before proceed to load more data.
However, if pull cable out from notebook and use only wifi - connection drop instantanously when press PgDn to load more data.
Thank you again! @alobpreis , @joshi