Its usually a problem with the encoding on the page itself. As in they probably copy pastad some code, of which parts are in UTF 8 & others are in UTF 16.
I don't know if IE chooses to ignore that error, or if mozilla chooses not to, you could check Google on that.
You could also ask on the website itself if other people with the exact same version as your Mozilla have the same issue as you do.
For a quickfix, try clearing all your cache & temp files & cookies, maybe something went wrong there while loading the page once & it decided to stick with it.