How do I get RES to open all reddit links in new tabs rather than windows?

I switched to Firefox recently from Chrome and for some reason, every time I left-click a link or a post's comment thread, Firefox opens it in a new window rather than a new tab like it does in Chrome, Opera, and Brave.

I've dug through the settings and options of both Reddit and RES in all three browsers and I can not for the life of me find an option that forces new pages to open in new tabs of the same window rather than new windows completely.

Where does it happen? Any time I use left-click to open a link or comment thread.

Screenshots or mock-ups na

What browser extensions are installed? RES, uBlock Origin, Moderator Toolbox for Reddit, Enhancer for Youtube.

• Night mode: true
• RES Version: 5.16.9
• Browser: Firefox
• Browser Version: 67
• Cookies Enabled: true
• Reddit beta: false