I like that I can pull a popup in only when I want to, not every time. However, this extension will move every active popup — there doesn't seem to be a way to target just one — and it seems to consider every window with a single tab to be a popup.

Good, but clicking the notification doesn't move it on Linux.

It would be nice if it would work automatically

Does what it says, nice and simple!
Would be really great to add an option to remove the context menu item; the notification is all I need.

Nice simple extension if you want to send the popups into tabs, but it does not force popups to start as new tabs which was my requirement.

For that it's better and simpler to go to about:config and editing "browser.link.open_newwindow.restriction" to zero "0"

It might be nice for a later release to add this and maybe configure which popups would come as tabs or which would be allowed as native popups.