I had the same problem.
Running firefox with root privileges (sudo firefox) worked, thus hinting that permission rights might cause the problem.
I do not have a "msfonts" subdirectory, but rather "windowsfonts".
My solution was therefore:
sudo chmod +r /usr/share/fonts/truetype/windowsfonts/*.ttf
I had the same problem. fonts/truetype/ windowsfonts/ *.ttf
Running firefox with root privileges (sudo firefox) worked, thus hinting that permission rights might cause the problem.
I do not have a "msfonts" subdirectory, but rather "windowsfonts".
My solution was therefore:
sudo chmod +r /usr/share/