Fullscreen Slider Buttons in Firefox / Android

Hello,

I have an issue with the prev-, next- and scroll-down-button in my Enfold Theme.
In Safari everything is fine, the entypo-fontello is perfect and the arrows are perfectly shown in the buttons.

But in Firefox or on Android mobile the buttons show no arrows but strange hieroglyphs or chinese characters.

I’ve tried some css fixes like …
.avia-mozilla select, .avia-mozilla .avia_ajax_form .select, .avia-mozilla .entry-content-wrapper select, .avia-mozilla .mobileMenu { font-family: entypo-fontello !important; }
… but this doesn’t work at all.

Do you have any suggestions to fix my problem?
Thank you so much!