Your comments

The helper updated to 4.85. I am seeing the subtitles listed in the menu now, so everything is great. Thank you.
Well, this is weird.
First. To answer your question, I'm using Firefox Ver. 37.0 and the version was 4.85. The reason I say "was" is because I decided to download and re-install the helper, and it's now saying it's only 4.80.
The good news is that I looked at the helper download options for a YouTube video and found the subtitle files were included in the list. Maybe I just missed it before or the selection got "fixed" when I re-installed the helper.
Other than the roll-back on the version, everything is great now.