Have no idea what to do to fix it except, possibly, a Firefox refresh or reinstall

CTRL + SHIFT + DEL brings up the Clear All/Clear Recent History dialog for me, depending on whether I cleared Everything or some time range, respectively, the last time.
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Brian - Windows 10, 64-Bit, Version 21H1, Build 19043  

It is the function of creative men to perceive the relations between thoughts, or things, or forms of expression that may seem utterly different, and to be able to combine them into some new forms--the power to connect the seemingly unconnected.

    ~ William Plomer