There's actually a hidden option for this. Perhaps it should be made more visible? If you want to give it a try:
(A) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.
More info on about:config:Configuration Editor for Firefox. Please keep in mind that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.
(B) In the search box in the page, type or paste browser.tabs.closeTabByDblclick and pause while the list is filtered
(C) Double-click the preference to switch the value from false to true
It's much time-saving to add a function that users can double-click the tab to close it(recently edge browser added this function that suits Chinese users who use their domestic browsers with this function)
There is a setting option in Microsoft Edge that can close the tab with a double-click on it.From my point of view:this feature accelerate the closing of used tabs,quicker than perform Ctrl+W to close or close it directly.
But Firefox hasn't got that feature,it may decelerate the speed to close the used tabs.So I suggest the developers adding it.