Noted in other discussions and Samsung's web site, read
In short there is no PC or a lot of RAM in the TV so it's a compromise or limited browser.
If the site wants Smart TV viewers they must test their site on the Smart TVs and stay inside the limits.
OR, do what Netflix did and make an app.
I am having Samsung Smart TV model UN55ES7150, Software version T-MST10PAUSC-1034.2, BT-G.
Every time I watch online movie through web browser, I get abruptly the following message
"Your last browser session ended because of lack of memory or another unknown reason. Do you want to restore your last session or go to your home page"
Earlier I was having issue of buffering as well but after upgrading firmware, buffering issue resolved but the above message still continue to appear. This is very annoying.