Only include Fira CSS on /unsupported/* route

[pdehaan]

Fixes #391

[ericawright]

Looks good. I also wonder if using Fira was intentional, since this is the only place it's used. But that's a question for @Pekochen, and in the meantime I see no problem with merging this.

[pdehaan]

Looks good. I also wonder if using Fira was intentional, since this is the only place it's used. But that's a question for @Pekochen, and in the meantime I see no problem with merging this.

I'd be more than happy to remove Fira. It feels a bit aggressive to display it only on that page. "Sorry your browser is unsupported, but here is an additional 170.75KB of fonts"...