Very nice add-on, thanks a lot!

I'm using it with firefox 68 ESR on a linux system with a 3-button mouse. I'm using only the "Long left-click" since the "Right-click" interferes with the context menu in an unfavorable manner.

My typical use-case: Scanning a news-portal, I open some articles in new tabs in the background via long left-clicks and then I read the articles in the tabs afterwards. However, there may be articles I want to read immediately, so I open them in a new tab in the foreground via the standard firefox middle-click shortcut.

Bottom line: Although this add-on aims at 2-button mice, it is also very useful for 3-button mice. It would be even more practical, if there were a "Long middle-click" option in the preferences: a short middle-click opens a link in a new tab in the foreground, a long middle-click opens a link in a new tab in the background. Such a feature would comply with the standard firefox mouse shortcuts. (Till the change to the WebExtensions API, the add-on "MClickFocusTab" provided exactly this feature - for me it was one of the most important add-ons. Unfortunately, it was not adapted to the WebExtensions API.)