Activate your CapsLock button. Using gnome-tweaks, remap your CapsLock to a Menu key, and then this extension works perfectly. Alternatively, choose a different key in the extension settings. Don't forget to log out and in again if you're updating the extension manually.
Note: Binary files aren't shown on the web site. To see all files, please download the extension zipfile.
You should use the gsettings instance you have created in line 26 (extension.js) instead of creating it again in line 52 (extension.js). I approved this one since settings is local in enable. Don't forget to null that out in disable, if you made it global in future versions.
Thanks for the super quick review(s)!
Captivate