I gave it 2 stars because the add-on compile and install worked without error. Otherwise is does not seem to work al all.

I am trying to make my firefox windows with lots of tabs land in the right Activity. I probably have an odd setup. Main screen is Screen 1 on a UHD monitor, Screen 2 is 1920x1080 monitor positioned to the lower right . There are 4 Activities and no virtual desktops. The hardware is Intel i7 with 32GiB memory and solid state drive.

Linux version 4.12.12-gentoo (gcc version 5.4.0 (Gentoo 5.4.0-r3 p1.3, pie-0.6.5) ) #1 SMP Thu Sep 14 10:42:39 CDT 2017

Activities handle single application windows for konsole, thunderbird, and ksysmon properly. They always appear in the proper activity at the correct location.

I was hoping the KDE Activities add-on would fix the problems with firefox. No such luck.

I compiled and installed the native part from git following the instructions provided. I verified that the proper firefox windows were in the proper activity. I logged out and in, Most firefox windows in each activity are located at the wrong position and have tab sets that were not in that activity when I logged out.
As an additional surprise, the the originally selected tab is no longer selected, Instead the rightmost tab is selected.