One thing to look at is in Tools -> Settings -> General Tab and check the box next to Open links in tabs instead of new windows in the Tabs section.

To force other things into new tabs, go to about:config and change the following to true:

• browser.search.openintab
• browser.tabs.loadBookmarksInTabs
• browser.urlbar.openintab

WARNING: Changing preferences through this interface not officially supported Hidden settings edited using the about:config tool are explicitly not supported, which means that Mozilla makes no guarantees they will be supported in the future, or that Mozilla will fix them if they break. Mozilla does not test these preferences, and will not in the future. That includes security and performance testing which these preferences may affect.

[Warning added by moderator]

Hopefully that helps, Mark H.

You can override how external links are opened via the browser.link.open_newwindow.override.external pref. If this pref has the default value -1 then browser.link.open_newwindow is used. The meaning of the value of browser.link.open_newwindow.override.external is the same as of browser.link.open_newwindow

• 1:current tab; 2:new window; 3:new tab;

So new Tab should be: about:config => browser.link.open_newwindow.override.external = 3

You can open the about:config page via the location/address bar. You can click the button to "Accept the Risk and Continue".

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

DISCLAIMER: modifying prefs directly via the about:config page is not officially supported and there is no guarantee that this will keep working in future releases or otherwise "breaks" Firefox.

Solved. Thank you guys!