How strange. Thought this is a general issue or 'feature'. Maybe you close it FF differently as me? https://support.mozilla.org/en-US/questions/1291164
How strange. Thought this is a general issue or 'feature'. Maybe you close it FF differently as me? https://support.mozilla.org/en-US/questions/1291164
However, they disappear and are not loaded anymore if you have multiple Firefox windows open and the window with the pinned tabs is not the last Firefox window one you close...