I'm not sure what the hell is going on here but I can't access most of Bitcoin websites , website that I have tried so far are Blockchain.info , Coinmarketcap.com , BTC.com , Blocktrail.com , Poloniex.com , Kraken , Wirexapp , CoinsBank , Bitmixer.io and the list goes longer ...
Firefox keep giving me the following error : The connection has timed out , The server at Poloniex.com is taking too long to respond. (All websites)
I always get the same error when I am having a slow internet connection.
Have you tried restarting your router or whatever your internet device is.
Bitcointalk.org does not require too mh data so you will be able to access it without any problem but id it is the sites that you mentiones it requires a better internet speed.