I have my browser.sessionstore.max_windows_undo in about:config set to 60 – it's been like this and working fine for several months. It's set to this high number because I use an assistive technology which creates a fresh pop-up every time I deploy it, and Firefox treats it as a browser window closure when I close the pop-up. Consequently, I can easily rattle through well over 25 window closures in a day. It's not necessarily that each window contains dozens of tabs and copious data, but nevertheless Firefox still treats it as a window 'within the meaning of the act'! I just went to reopen one closed window from a couple days ago which ''did'' contain many tabs (partly why I closed it in the first place), only to find that the 'recently-closed windows' context menu is now only showing 20 windows (18 of which are the aforementioned pop-up assistive technology windows) The really ''vital'' window that I want to reopen is not showing. I've double checked in about: config and the browser.sessionstore.max_windows_undo is still set to 60 windows; nothing has been altered or reset. I updated Firefox to 147.0.4 yesterday evening, but the problem existed before I updated Firefox, and is still in evidence since updating. Two questions: 1) Why is the Recently Closed Windows context menu not showing the full number of windows it has been successfully doing with no problem now for months? I used to have to scroll down to access the full extent of the 60, but they were always '''there'''. 2) Why has it arbitrarily changed to 25 windows? 3) [I lied – Our chief weapons etc...] Is there a way that – given about:config still implies that the most recent 60 windows are retrievable – that I can access beyond the 25 windows limit that are currently showing as reopenable? Thanks very much (And yes, I already have things like ''OneTab'' and ''Tab Session Manager ''add-ons, but disabled those just before closing the important window, because I was trying to locate which add-on was draining the CPU. I assumed my 'recently-closed windows' buffer of 60 would suffice while I disabled the add-ons.)