2 of our staff tested your site on Firefox (one Windows and one Mac) and neither of us experienced the issue – the site loads fast and perfectly on first load.
We haven’t received any other similar reports either so it’s definitely a little tough to debug and identify the problem.
Do you see the same issue when using Private browsing mode for FF?
if i slow my network down i can see the FOUC ( Flash of unstyled content ).
The most likely culprit is the Litespeed cache, as it could interfere with resource loading to try and reduce render blocking.