Glitch or something?

I'm on a mac and when I click on the RuneScape part of the screen, it has like an outline, and when I move the camera angle it gets stuck in one position. For example if I push the left arrow key the game won't stop spinning left. What is going on?!? I remember this exact thing happened to me on a private server I played.

 

Download a different browser, usually fixes things like this.

 

Not even close to a glitch...

Double tap the arrow keys will fix this.

 

What is it then? And that didn't work.