Been using Tree Tabs for several years without a hitch.

Anyone who does research online and has many research projects running at once likely has dozens if not hundreds of tabs open at any one time. Tree Tabs makes navigating hundreds of tabs easy and manageable.

Some people are saying this app frequently crashes, but it is NOT the case for me on an old laptop running Windows 10.

Firefox is a memory hog, so perhaps having problems are running out of memory? I am using Tree Tabs on an old HP Elitebook G3 laptop with 16GB of RAM and never have a problem with Tree Tabs. On occasion Firefox will bog down to the point of not being usable due to it not freeing up RAM properly, in which case I simply close out of Firefox and restart and all tabs are restored.

TIP: If you are running multiple instances of Firefox (i.e. multiple open windows) and want all the windows reopened upon restart, close all Firefox windows at once by using Windows Task Manager (shortcut Ctrl + Shift + Esc) and select Firefox from the list of Apps and click End Task. This will close all windows at once and when you restart Firefox all windows will reopen.

Tree Tabs add-on makes Firefox one of my favorite browsers (although I prefer Brave for its speed, better memory management, and some privacy features [although Firefox Containers is a plus for privacy]).