I’m viewing your site on Firefox and I don’t see this issue.
Here’s how it looks like on my end using Firefox:
https://share.getcloudapp.com/xQuYzzrY
As you can see here, its display the correct font even when I’m on a Firefox browser.
That said, perhaps you’re viewing a browser cached version on your Firefox browser.
Can you try clearing Firefox’ browser cache?
Here’s how to do it – https://support.mozilla.org/en-US/kb/how-clear-firefox-cache
You then try to check again if it displays properly on your end.
Let us know. 🙂