Paste popup not working in Firefox

I'm getting an error when pasting using CTRL-V from Firefox when pasting from Word. A security popup pops up (surprisingly :-p) when I use the paste button, but if I use CTRL-V it does not pop up and it pastes directly causing all manner of problems. How can I make the popup pop up when pasting using CTRL-V?

Muchas gracias por la ayuda.