Menu doesn't dropdown in Firefox

Hi guys!

I’m having this issue with Platform theme:

Main menu and submenus in it show correctly in Safari and Chrome BUT not in Firefox. Firefox doesn’t even show the arrows indicating there are submenus inside each item.

Any clues please on how i may solve this?

You may find a link to my blog in pastebin here. (Menu is not available on home page, so you should click on any link to enter the blog and see the menu).

Thanks a lot for your kind help!