Android - Facebook mobile website tries to open Messenger all the time
Facebook started forcing this change a couple of months ago. There's nothing anyone can do about it. I find it rather annoying myself which is why I switched to a Facebook wrapper app like Swipe It has a workaround for this behavior. I suggest you do the same.
Try using https://mbasic.facebook.com It's not as pretty and you have to click "See Older Messages" and "See Newer Messages" a lot, but it's quite functional and fast.
Just realized I was responding to the duplicate question, but here's another solution: Use Adblock Browser. It's a free browser that disables a lot of ads, and even though some mobile sites might act strange (which is why I still use Chrome), it stops facebook from opening up the Play Store. Hope that helps.
Edit: I've been told that other mobile browsers, namely Dolphin and Lightning, don't have the auto-linking.