Tempera displaying Symbols incorrectly in Firefox & IE (but not Safari)

Under construction, my site (huch.ch) was displaying correctly. After changing on public domain and installing a “www.”-Forward the symbols on my site no longer looked right. In particular, the magnifying glass next to the search bar, the down and the up arrow in my main head menu were replaced with a ugly symbol (which now displays as something like a a box with 4 letters in it on Firefox or something like a little box with a cross in it on Android Smartphones; on IE no more symbol is visible…).

My web-designer then replaced the wrong symbols with other unicodes for similar symbols. But by installing the new tempera update the replaced unicodes were re-replaced and the wrong symbols were coming up again.

My web-designer and his programmer couldn’t find any solutions. Does someone know the problem? And is there a solution for it?

Thanks for help in advance!