After reading up on the topic of https everywhere features, I'm pretty sure it is not implemented in any browser. At least not in the way it would automatically detect if there is a https redirect possible. Extensions like "HTTPS Everywhere" build on YOU sending in rulesets for the redirects.
Your setup looks good imho. Only weird thing is, that you basically also attach the https redirect to the router on the websecure entrypoint. But I'd guess this would be ignored then. And if it wouldn't, why would Firefox be the only browser having issues?
Maybe something with caching in the browsers? Have you tried in a private window? Or deleteing browser data?
Have you tried using plain old curl? Like curl -v http://qa.domain.com?
In general I do the https redirect on the entrypoint static configuration in the traefik configuration file. Maybe that is worth a try? Of course this only works in case you redirect all of your non-https traffic to https. But if you do you can find my static entrypoint config in this issue.
Another idea that came to my mind was maybe some proxy config, that you have setup in all other browser, but not in FF?
Sorry, I don't really know a solution there. Just throwing in some ideas.