While not updated in a while, this add-on still works perfectly with 102esr. This add-on is worth its weight in gold for tweaking CSS. Mozilla really should provide an about:config setting to force cache refresh. Until then, this add-on is perfect for the job. It goes one better by allowing per-domain cache control. Very nice.

Does the job. I was getting fed up with FF just ignoring the "disable cache" feature in "Network" developer tools.