Custom font not loading on Frontend

Hi !
I've looked through all of the support topics and haven't been able to find a solution. I have uploaded several custom fonts, their WOFF files in a separate FONTS folder in my child theme. In my CSS, I've called each font, and have verified each link (when I copy/paste the link in my browser, the font downloads).
Unfortunately I can't seem to figure out why they aren't showing up on my site (I've just migrated from localhost to Live, and have verified the URLs). It works on my desktop Chrome browser, but not in Firefox nor on mobile (Android phone using Chrome as well).

If you can help me see what I am missing, that'd be great !

P.S., where should I put websafe fallback fonts for these custom fonts ?

Thanks for your help