Is there a way to do that? Implementation doesn't matter too much (config file change, restart, add-on, whatever). What I'd like is a way to - ON REQUEST, as one-off - to clear out my list of recently closed tabs and windows from the current section. Problem is, that this same nifty feature will still keep the closed tabs/windows - a lot of them - in the session, because that's what it's set to. However, sometimes, I close a gazillion tabs in several windows in an effort to clean up my Firefox, on purpose (this should improve performance and memory utilization). This is something I like, as a way to be able to recover from accidental/thoughtless closing, so I don't want to set that to zero. My Firefox (Windows, latest version - 50+, Session Manager Add-on installed) is configured to keep X recently closed tabs per window and Y recently closed windows in the session.