Tab and window management
1. Bookmark all tabs
You are likely familiar with Command-D to bookmark the current page, but did you know that Command-Shift-D lets you bookmark all of the tabs in your current window? I find it a huge help to bookmark a group of tabs so that I can close them in order to minimize the number of tabs I have open, which typically are legion.
2. Open link in new tab
Some links are coded to open in the current tab while others open in a new tab. To take control of this behavior, press Command when you click a link to stay on your current page while opening the link in a new tab in the background. Likewise, use Command-Shift-click to open link in new tab and switch to it. Also, Shift-click to open a link in a new window. See more here
http://isaacfortune..com.ng/2016/07/21-firefox-shortcuts-for-mac-os.html