The problem seems to be caused by the method you are using to include the css:
<link type="text/css" media="all" href="https://innovativeblogger.com/wp-content/cache/autoptimize/css/autoptimize_9b326d6258c2a89311e990647700d928.css" as="style" onload="this.rel='stylesheet'" rel="preload" />
I don't believe the onload works properly for link elements in Firefox and it seems that the height of the sticky nav is dynamically calculated before the css rules have been applied and without styling the height is a massive 342px.
If I copy your page and put the css in the head of the page as normal Firefox works fine.
I don't know enough about the preload technique (or why indeed its needed) but perhaps this SO answer has some hints or you may need to ask in the JS forum for a more foolproof method of whatever the code is trying to achieve.
Once you start fiddling with the normal methods of delivering css you will run into problems.