As per old thread at: https://support.mozilla.org/zu/questions/1365405 which has since been archived. As of version 113, this solution is being suppressed. I occasionally see the x appear briefly on the left when a tab is selected, but then it reverts. So far I have not been able to work out what setting is overriding this function, so I've just rolled back to 112 and used the "--allow-downgrade" flag on the firefox shortcut so I can still load my old profile, but understand this is not a safe option in the long term.