Chrome and Firefox now have implementations of the split view feature:

• Firefox: https://support.mozilla.org/en-US/kb/split-view-firefox (announcement: https://blog.mozilla.org/en/firefox/split-view/)
• Chrome: https://support.google.com/chrome/answer/16971124

Early support for the splitViewId concept was added in #842 with https://github.com/w3c/webextensions/blob/main/proposals/split_tabs_proposal.md

Although it is possible to detect the presence of split views, it is not possible to explicitly create or remove split views. This issue is a placeholder to have discussions.

Relevant scenarios:

• Given a tab, create a split view (defaulting to whatever tab the browser shows by default).
  • Question: should there be a way to open the split view to the left or right? Or should extensions wishing to control that behavior make an additional API call, e.g. tabs.move?
• Given two tabs, put them in a new split view.
  • Edge case: what if either is already part of a split view? What if the tabs are not already adjacent to each other?
• Given two tabs in a split view, remove the split view (= transition splitViewId to -1).

Firefox ticket tracking the implementation of this: https://bugzilla.mozilla.org/show_bug.cgi?id=2016928