I agree with @gffsdss... The Japanese theme is exactly how the Canadian theme should have been designed with a white background and red maple leaf. The predominant use of red is hard on the eyes – taking focus away from web page content that Firefox is parsing.
As others have said: too much red; hard on the eye; overwhelming; black typeface very unsuitable for a red background; just hard to read and unattractive. Also, cutting off the top points of the maple leaf is weird (to Canadian eyes, anyhow). The Japanese theme shows exactly how this theme could have been executed: white background/red maple leaf. Simple, clear, attractive - done.