Fresh installation of Flarum and accessing it via Firefox didn’t display icons, I could not login. Seemed like CORS problem.
Found on the forum:
https://discuss.flarum.org/d/22770-oops-something-went-wrong-again/14
In your .htaccess file, after RewriteEngine on, add something like this:
RewriteCond %{HTTPS} off [OR]
RewriteCond %{HTTP_HOST} ^www\. [NC]
RewriteRule ^ https://yourdomain.top%{REQUEST_URI} [L,NE,R=301]
