Firefox open new tab problem

[G-MAN2004]

This has only just started recently but is truly annoying. I press the wheel on my mouse to open a link in a new tab, but now most of the time when I press it, it opens the link up twice (two tabs). Why is this?

Thanks.

 

[G-MAN2004]

Anyone? It's driving me insane having to keep closing the extra tab.

 

[G-MAN2004]

Yep, most recent version.