Nice extension, thanks! :) But I can't figure it out how to use "Position" and "Relation" options. For example, how should I set it up to: 1) when closing current, select parent tab; 2) if no parent tab exists, select left tab; 3) if the tab to close is leftmost, select right tab?

Doesn't work correctly if you're using UnloadTabs. You can use another addon called "Unload Tab from Context Menu" and then it's fine.

I find the default Firefox behavior really annoying and this extension fixes it for me. I used to get this functionality as part of the Tab Mix Plus extension but unfortunately it doesn't work with newer versions of Firefox.

There seems to be a conflict with another extension that deals with tabs, the Unload Tabs extension (https://addons.mozilla.org/en-US/firefox/addon/unload-tabs/). With that extension enabled, this extension only works sporadically. If this extension doesn't work for you I would try disabling any other extensions that deal with tabs and see if that fixes the problem.

Original review: Doesn't work reliably under Firefox 77. Often the configured tab is briefly selected, then Firefox switches to the tab to the right of the closed tab. But I love the idea!

It was hard for me, to find out how it works. It would have been easier, it the column "relation" were on the left position und the column "Positon" were right of it. So I would have known, that Relation is the main criteria.
If you add some examples to the description, the configuration would be much easier, to understand.
With a better description I would have rated 5 stars.

Great. But is there a documentation??

Choosing Last accessed tab and Skip hidden works great most of the time. It goes back to the previous active tab without reloading it. Seems like this should be the default Firefox behavior, but isn't for some reason. Skip hidden is needed with the Simple Tab Groups add-on to avoid switching tab groups unexpectedly.
Bug: In FF 65, select Left tab doesn't work if the browser has just been started. It always defaults to the right tab.

Great add-on does what it says.

Generally works fine but flashing, when switching from a tab selected by default, sometimes can be really annoying.
And if the default selection is taken from a youtube's tab, it still starts playing the video.

I understand that most likely FF doesn't provide any better way to do this in the moment but that's an issue nevertheless.

Where is the "Preferences of it in the Add-ons Manager" you refer to? I have installed successfully the add on but I cano not fine the settings anywhere, in the adons manager when I click options I just get the basic info

This should receive five stars for functionality and simplicity. However, the selected tab switches erratically when clsing the last tab of a node with Tree Tabs. (I guess I'm being a little picky)