How do I get Firefox to open a link in a new tab?
Open a new tab in your browser, type about: config in the address bar, and hit the Enter key.
Click on Accept the Risk and Continue.
In the Search preference name bar, look for the parameter browser.search.openintab. It has to be set to true (false by default). Just click on the toggle from the right side.
Do the same for browser.urlbar.openintab, browser.newtabpage.enabled and browser.tabs.loadBookmarksInTabs .
Search for browser.link.open_newwindow and check to have the value 3.
Also, search for browser.link.open_newwindow.restriction to have the value 0. To modify the value double click on it and then click on the check marked sign on the right.
Restart Firefox to keep the changes.
