It was set to "true" which is default. I set it to "false" and closed/restarted Pale Moon. I had my down arrow at the bottom of the tabs back and when I clicked on it, I got the vertical list. Thank you!
That setting is not in Fx 24.6.0 ESR about:config. Is that setting new in Pale Moon 24.6.2? Ahh...googling told me that it was removed in Fx 21 which I never had. I had Fx 17 ESR before the current Fx 24 ESR. If that was in Fx 17, I guess Tree Style tabs over rode it as I always saw the tab list. (Or maybe I changed the setting to false in Fx 17 ESR and then forgot about it so I didn't think about it maybe being in Pale Moon).
I don't think I set "browser.allTabs.previews" to false in the earlier Pale Moon I had because I didn't know about it and I had the list of all tabs shown then so I wonder what made it change when I upgraded Pale Moon? I suppose Tree Style Tabs maybe over rode that setting in the previous version of Pale Moon? Ah well, I'll probably never know but the main thing is that it is fixed! Again, mahalo!