I have been wanting the ability to merge two window’s collections of tabs in Google Chrome for some time now, because moving one tab a time from one window to another is tedious at best.
I thought I’d need an extension for it, but it turns out that you can already do it in Chrome without any extra extension! I found this tip on the Google Chrome Product Forums, which tells how to do it:
Left-click the first tab in the window you want to merge. While holding the shift key, left-click the right most tab. All of tabs for the current window are now selected, so you can drag and drop them as as group on the other window.
One thing the tip doesn’t mention is that you have to keep holding down the Shift key while doing this process to move all tabs, otherwise it shifts back into single-tab-move-mode.
Hope this helps!