Help link tries to open second instance of Firefox on Mac?

I have Firefox set as my preferred browser on Mac OS X. When in Fusion if Firefox is already open, as it usually is for me, if I select Help from the Fusion 8.2.1 build 6 Help menu it tries to launch a second instance of Firefox and then I get an error dialog:

Close Firefox
A copy of Firefox is already open. Only one copy of Firefox can be open at a time.

It seems like it's not invoking the link to help properly. If Firefox is open then the help link should just open when triggered from Fusion. It shouldn't try to force a new instance of Firefox to open. It should just tell Mac OS X to open the URL and Mac OS X would then just pass it to the open Firefox.

It's likely Firefox is set to be your default PDF reader.

So Fusion is launching it to open the Help PDF.

Try to change the default application to another one.

I believe Preview is set to my default PDF viewer (and Firefox is set to be my HTML viewer). But I'll try that to confirm to help isolate the bug. Fusion should not be launching anything for this though. It should just send the open link to the OS and let the OS handle opening the file and launching an app if necessary. That way Mac OS X will open the file in whatever app is set to handle that file type and if that app is already running it will just open the file. On Windows you can have multiple instances of an app running but on Mac OS X that's not normally allowed.

OK, I ran a few more tests on this. It's strange.

My default PDF viewer is Preview. Double-clicking on any PDF files opens them in Preview.
My default HTML browser is Firefox. Double-clicking on any http URL opens them in Firefox.

Clicking the Help link in Fusion launches Firefox and opens the link in Firefox if it's not running. It throws an error if Firefox is already running.

What's strange is that if I drag the link that Fusion opens in Firefox right out of the Firefox address bar to the desktop. And then double-click on that file reference, it opens up in Preview, not Firefox. So I'm not sure why Fusion is trying to launch Firefox first.

file:///Applications/Blackmagic%20Fusion%208/Fusion%208%20User%20Manual.pdf#nameddest=05%20Fusion%208.indd:.96846:3968

This bug still appears in Fusion 9 on Mac.