409 errors and reload loop when logged in to a wordpress website - only in firefox

When I log in as admin to my wordpress website, firefox gets stuck in an endless reload loop. https://imgur.com/hnjbGGe Sometimes if I clear the browser history or open a private window, I can successfully log in and load a page - once. The page seems to load normally but there are 409 errors shown for many of the files in the developer tools. https://imgur.com/uTugRTC If I reload the page again, it goes back to the endless loop. This started when I installed a wordpress caching plugin, but the problem is specific to firefox, so I don't really know whether firefox or the plugin is actually responsible. How could firefox be getting 409 errors when other browsers get normal 200 responses for the same resources? Why is firefox triggering this reload loop, and is there a way I can stop it?