There is the browser.tabs.selectOwnerOnClose pref in about:config that when set to true might work to return to that tab.

You can also open tabs next to the current tab via about:config.

• browser.tabs.insertAfterCurrent => true
• browser.tabs.insertRelatedAfterCurrent => true

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

Thank you @cor-el The browser.tabs.selectOwnerOnClose option has specific use cases and it looks like I would have to disable other desirable option(s), so it's not a solution. The opening of tabs is not part of the problem. I don't know why such a configurable browser doesn't have an option for this or do it right. I almost never want to go "next" rather than previous and lots of people ask for this.

Enable "Ctrl+Tab cycles through tabs in recently used order" in settings and use it to switch to the last viewed tab.

I do this but it's an extra step which I'd rather avoid. There should be an option. There are so many; what's another one? Other browsers (Opera, I hear?) do it right.