I also removed my tab close buttons after the video, and the new tab button (which was much easier to do), but now when I have ~8 or so tabs open, firefox doesn't react to middle-clicks in the little space that's left. I've tried putting a "flexible space" there from the customise menu, but that doesn't let me open new tabs by middle-clicking it either.
Any ideas to fix this would be appreciated, I'm just using Ctrl + t to open new tabs past 8 in the meantime.