Thanks. Try this. Click the 3-horizontal-bar icon at the top right of the screen and select Options.
On the left, select Privacy.
under History, set Firefox will: , using the drop-down arrow, to Use Custom Settings for History
click Show Cookies
click Remove All and close that window.
then, click Advanced on the left then Network at the top.
to the right of Cached Web Content click Clear Now
you may have to click more than once to get it down to near zero.
Close and re-open Firefox.
Because you're removing cookies you'll likely be asked to log in to those pages again.