FireFox will not open some links in a new tab, only in a new window.
Anytime I attempt to open a link in a currently open page, it will only open in a new window, never a new tab, unless I middle-click or right-click and click on "open in a new tab."
Opaite Mbohovái (1)
Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).
See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems
If it does work in Safe-mode then disable all your extensions and then try to find which is causing it by enabling one at a time until the problem reappears.
You can use "Disable all add-ons" on the Safe mode start window to disable all extensions.
You have to close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")