You could try disabling fonts .. if you have installed any.
In Font Book, select your user, select there all fonts, and click on the "v" button which will disactivate the fonts. (All system fonts will still be active, they cannot be disactivated).
If Safari will behave correctly, it was caused by a bad font. If you have a lot of fonts, you can enable a part of them, test if the issue occurs, enable or disable some more until you would find the guilty one.
And if it wasn't the font, let us know so can test more.