Font Book issue / crash & Safari

[Medic]

I recently installed a font collection in my Font Book and now it has updated Safari's default Font, even though the default is still Times, on most sites, it is a wierd modern, almost unreadable font...I've tried changing, but this crashes Safari. I installed Firefox, and the font has been applied automatically as well. If I try to open Font Book, it'll crash... Any advice?

Many thanks!