The two aren't connected.
Firearms have been tightly controlled in UK for well over a century, but the Dunblane shooting lead to really tight control. Basically, even gun club shooters had to hand in their firearms. Absolutely no automatic or semi-automatic weapons.
The Facebook thing is about incitement to violence...
Graham Linehan was arrested on suspicion of inciting violence and bailed pending further investigation.
www.bbc.co.uk
Judge for yourself whether he was inciting violence - most of the British public have made up their minds.