The people that are likely to get affected by this are Windows users who elect to use the Zip download - as they get no help folder (and alpha testers who also get no help folder).

I doubt that many sane folk would diddle around and rename, move or delete the help folder - and still expect things to work as normal.

There is a much easier way of reproducing this than in the steps.

1) download a Zip version of Audacity on Windows
2) launch audacity
3) click Help>Manual several times
4) observe you get several "Help on the Internet" windows

DEVEL - FIX MADE
https://github.com/audacity/audacity/commit/aee4e5deaa2dc39fcdf4fd7854f5a0b3d69df064

(In reply to James Crook from comment #2)
Testing on W10 with audacity-2.3.3-alpha-311-711e600eabab96102f55e5ef09631189a355ee77

alpha version - so no help files installed

I no longer get multiple help dialog windows - just a single one
a) with Help>Manual
b) with repeated clicks on the "?" help button in Analyze>Contrast

Looks to be properly fixed on Windoes

Testing on macOS 10.14.5 Mojave with 2.3.3 Mac alpha jc005 of 01Aug19

Tested by temporarily renaming the help folder

As with Windows

I no longer get multiple help dialog windows - just a single one
a) with Help>Manual
b) with repeated clicks on the "?" help button in Analyze>Contrast

Looks to be properly fixed on Mac

James has marked this as single platform test OK - so as test properly in Win and Mac I shall close this