In Tridactyl, you just push f, which allocates each key on the keyboard to a visible link on the screen. So to reply to your comment, the keystrokes were

>fu (click 'reply') >ff (select textbox) >ESC (deselect textbox) >fg (click 'reply')

and a lot easier- not to mention, less RSI-inducing- than mucking around with a mouse, or trackpad, or trackpoint, trying to aim a little cursor at a little box multiple times in a row.