I thought it was my Firefox-based browser, but have had similar ‘changes’ with a Linux browser. Sometimes when I refresh the screen, either the Articles-Activity-Comments tab changes and/or the Brevity: Headings-Text tab changes.
This has been going on for a couple of months.
I formerly used an IE-based browser (I still use it on my laptop and does not seem to be subjected to such automatic changes), but FR seems to no longer support log-ins with IE/IE-based browsers.
I just upgraded my Firefox browser on a different computer, maybe that was the cause?