Hi

This is not currently possible in Firefox for Android, but is something that we look into include in a future update.

I'm surprised to read this. Normally links open by default in the same tab. Web pages can decide whether a link opens in the same tab or a new one, does it really happen to you no matter which site or link? Then you might want to close and reopen Firefox (or even uninstall and reinstall Firefox) in case it's a temporary bug on your system.