Vivaldi has a built in tab management feature that allows movement of tabs to any other open browser window. This is a drop down box option when you click on a tab. There is a drop down box option on Firefox tabs that allow you to move a tab, with three different options, “Move to Start” meaning the first tab in the tab row, “Move to End” and “Move to New Window”. What the last option does is it creates a completely new window for that tab. What Vivaldi tab move option offers is to move the tab to a completely new window, but it also displays a list of existing open windows that the tab could be moved to. I have not found any Firefox extension that does this. There are several that create new “containers” in which to place tabs for security purposes, but nothing as simple as the Vivaldi tab move function. This may be a game changer for me. I was on Vivaldi for a while but was lurred back to Firefox because of the security and privacy policies, but now, I am going to check if I can Vivaldi can equal those policies.
Have you tried:
https://addons.mozilla.org/firefox/addon/tab-mover/ (page context menu)