Manually Sort Folders wasn't the only add-on that v115 broke. And I didn't care for the way the menus were organized at the top. So I too downgraded to v102 and wait until some new add-ons resolve these issues.
Kudos to @Itagaki for a great add-on, but it shouldn't be necessary. It should be integral to T'bird. Too much work for an independent developer to keep up with code changes that break the add-on.
