A Firefox Quantum extension designed to make interacting with tabs across multiple Firefox windows, spread across different virtual desktops/workspaces, easy.
Get it from addons.mozilla.org.
Press Alt-Space (Ctrl-Space on Windows) to launch the Palette. In the Palette, you may search for a tab, regardless of where it is. Press Enter, or click the tab, to switch to it. Hold Shift while pressing Enter, or click the "paste" icon next to the tab, to "teleport" the tab into the current window. The tab will be transferred with no loss in history or other state. Finally, you can close tabs by clicking the close box at the right side of the tab in the list.
To build this extension, simply run:
$ yarn
$ yarn build
inside the project directory. It will create the output file
web-ext-artifacts/workspaces_for_firefox-${VERSION}.zip
.