browser.tabs.insertAfterCurrent does NOT work as I expected. If I middle-click to open, say, 3 links from a page, the tab order will look like this "(current) (1) (2) (3)". browser.tabs.insertAfterCurrent works only when using Ctrl+T or clicking the "New Tab" button.

But this extension works perfectly! If I middle-click to open 3 tabs after installing this extension, the final tab order looks like this: "(current) (3) (2) (1)" i.e. the last opened tab is closest to the current tab.