Fonts differ across platforms?

I’d been using wanikani on firefox, running on ubuntu, for ages.
Now I’ve finally gotten a new computer (windows 7) and am still using firefox.
However, the font that hiragana/katakana is shown in has changed. Is there any way to fix this?

Old computer:

New computer:

I do not know how to fix that, but did you see it this way: if one of your goal is to be able to read japanese eventually, you should get used to more than just one font.

I know, I just think it looks nicer.
It would be cool if the font changed randomly to different font styles actually, that would be very useful.

For WaniKani Userscript, there is Jitai.

How do I use this?

Yeah I use Jitai, it’s great!

EDIT: Ninja’d by Plantron
You go there Jitai (字体): The font randomizer that fits