Firefox should always open things in a new tab.

[Bob_Loblaw]

Thats all, it should always open in a new tab, I loose track of so much because of this and it is insanely frustrating.

[PedroSaldanha]

You can open links on new tabs by pressing the mouse's middle button. Just press the scroll. If you are using a touchpad you can press in the middle of it.
I believe this can help you if you want to force Firefox to open every link on new tab https://support.mozilla.org/questions/1258193