FireFox keyboard accessibility issue

We have built some simple workshops in Storyline that need to be WCAG AA compliant. They are keyboard accessible in Chrome and Edge, but in FireFox, we have a bunch of empty tab stops between the website and the beginning of the Storyline workshop. It doesn't matter if it's published to ScormCloud, Articulate Review, or our LMS--the tab stops occur each time.

https://360.articulate.com/review/content/80c9d283-6942-4674-8aed-8e287dd43739/review

So if you visit this link and start tabbing to start the workshop, you will have to go through 11 empty tab stops before you can Play the workshop. On every slide, if you try to Tab from the beginning to the end, you will run into those empty tab stops.

We noticed that the number of tab stops correlated with the number of video slides we had. If we had two video slides, there are 3 empty tab stops; seven video slides, 11 empty tab stops; twenty-two video slides, 24 empty tab stops. So we think the Tab is finding all the video names behind the scenes--but it is not identifying them.

If anyone has any insight into how we can prevent this from happening, we'd be so grateful. We have been having issues with iPhone VoiceOver navigation too, and we wonder if this is the same thing.

The STORY file is huge, but accessible here: