I am running Firefox 52.0.2 on Arch Linux and although on the system (e.g.: in Nautilus) I have Japanese characters showing fine, in Firefox they are unreadable because all that is shown for them is this:
This will be because I do not have the font installed which allows the showing of Hiragina, Katakana and Kanji installed for Firefox. But the problem is that I am not entirely sure about how I get this for Firefox. I tried installing the Japanese dictionary in Firefox, but that didn't seem to make any difference.
So what do I have to do and install to get them to display properly? Because in this form it is obviously very difficult to read and write them.