Excellent, with minor flaws Rated 5 out of 5 stars

The Firefox Session Manager add-on is necessary for those who do extensive research online. If many Firefox windows and tabs have been open for several days, through several system hibernations, Firefox becomes unstable, and even corrupts the Microsoft Windows operating system.

(The Firefox browser instability and memory hogging has been reported many, many times over several years, but has not been fixed. The problem is especially severe when more than 20 Firefox windows are open, with 5 or more tabs in each window.)

Using Session Manager, when Firefox becomes unstable it is possible just to re-start the Windows OS. That is seen by Session Manager as a Firefox crash, and all Windows and tabs are saved automatically. When opening Firefox again after re-starting the OS, Session Manager then offers to open all Firefox windows and tabs as they were before re-starting. That allows researchers to continue from where Firefox became unstable, with a fresh initially stable instance of Firefox.

Firefox Session Manager is not perfect:

1) In Firefox > Tools > Session Manager, 3 menu options are at the bottom of the list, Open Session Folder, Session Manager Options, and Reopen Closed. If there are a large number of session files listed, those 3 menu options are below the list of old session files, and may be hidden if many files are displayed.

All menu choices should be grouped together at the top. The list of files should be below the menu choices.

2) There is good documentation of Firefox Session Manager at http://sessionmanager.mozdev.org/options.html. However, the keyboard shortcuts available in Firefox > Tools > Session Manager > General > Keyboard Shortcuts are not explained.

It is possible to write Ctrl, Alt, and Shift for the Control, Alt, and Shift keys: Alt+Ctrl+Shift+M means holding down the Control, Alt, and Shift keys simultaneously and pressing the M key. Or, you can just press those keys, making sure the letter or character key is last.

Session Manager apparently does not accept key combinations that include the Windows key.

This review is for a previous version of the add-on (0.7.5).  This user has other reviews of this add-on.