How can i merge 2 windows in Firefox Quantum, i.e. move all tabs of these 2 windows to 1 window?

I have many Firefox windows open and want to merge 2 of them. So far Web searches merely turn up extensions like these (1, 2) which seem to merge all windows. I have been looking at the API docs but can't figure out how to use these functions from the script console (it says "ReferenceError: browser is not defined").

  • 1
    I requested this feature and offered a donation. Please join me and express your support there if you would also like to see it.
    – AdamS
    Aug 12, 2018 at 10:59
  • This can now be done natively in Firefox. See update to DrMoishe Pippik's answer.
    – fixer1234
    Apr 2, 2019 at 20:30

2 Answers 2


Easiest might be just to drag-and-drop tabs from one instance of Firefox onto the other. That gives you control of which tabs to move and in what order they appear.

A multiple tab selection feature was added to Firefox in version 64. If you have a large number of tabs to move and want to do it in bulk, select the first tab, then shift-select the last tab to select the entire range (you can also Ctrl-select individual tabs to create a collection of selected tabs). Then drag the lot to the other window. So moving all tabs from one window to the other can be done with three mouse clicks.

  • 1
    Yes, i have enough tabs open to make this inconvenient, so am hoping for a programmatic method to merge windows. Jul 21, 2018 at 6:26
  • 3
    Hope you don't mind that I updated this for the new feature. It was already the right answer. :-)
    – fixer1234
    Apr 2, 2019 at 20:28
  • @fixer1234, Thanks for the edit. +1 Apr 2, 2019 at 23:48
  • 1
    Thanks, the multiple selection works for me! Feb 5, 2020 at 22:07

For Firefox you have an extension:

and for Chrome I'd been using for years:

  • Alas, merge-window merges all windows, not merely 2 given windows. Apr 2, 2019 at 19:09
  • Yes, both of these extensions merge all tabs scattered trough all windows into a single window
    – elMestre
    Apr 4, 2019 at 8:41

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