How do I force Firefox to check for a new version of page (browser.cache.check_doc_frequency doesn't work)?
I realized later what's going on. If I close the browser with tabs open, and then reopen the browser so that it reloads those tabs automatically... the tabs don't all get auto-refreshed. So I was viewing e.g. unrefreshed reddit. If I open a new tab, or close all tabs and then visit the page... it loads the freshest version.