c6223d7101
To ensure that a group ends up at the position specified by `index`, this patch adjusts the index when the tab group moves to the right. Before this patch, the tab group appeared at a too low (left) index because the original logic did not account for tabs shifting after a repositioning to the right. This also introduces stricter validation for moving tabs near pinned tabs or other tab groups. Previously, the tabbrowser internals adjusted the index as needed to fit adjacent to pinned tabs or groups. Now, the extension API throws an error. The new behavior matches developer expectations and Chrome's behavior: https://bugzilla.mozilla.org/show_bug.cgi?id=1963825#c9 Differential Revision: https://phabricator.services.mozilla.com/D249493