Hey, this is wonderful and it's also the only thing I can find that has the function on Firefox which mimics "Open as Pop-up" from Chrome.

The only issue I'm having is that the context menu "Open Page in Main Window" never seems to work. The pop-up window stays and clicking that option does nothing. In case it's relevant, my use-case here is that I like pop-up windows as semi-permanent ways to display some windows on my screen in a clean, clutter-less fashion to keep my interactions with these windows as focused and clean as possible.

If you have any suggestions for how I can make the option to reopen the page in main window work correctly, I'd really appreciate it!

Amazing add-on. and some suggestions:
1. drag to open in popup window
2.remember the popup window size if resized manually