Right clicking on menu bar item behaves unexpectedly and loads a page

When I right click on an item in the menu bar (such as Distributions or Projects) it loads that page, without you having selected anything in the context menu.

Normally when you right click on a link you get a context menu with options such as "Open link in New Window" and this is the behaviour I would expect from any link in launchpad. Right clicks don't normally do anything apart from display the menu until you select a menu option.

When you right click on the menu bar you get a different context menu without the option to open link a new window (which is what I was looking for) and it starts to load a new page. Right clicks are behaving like left clicks.

(I'm using Firefox 1.5.0.5 on Dapper)