Accessible Text Not Working in Storyline 360

I've been trying with little success to replicate the accessible text functionality demonstrated in this support article. 

After adjusting the font controls in Google Chrome, the slide text in the published course does not change size. The leading (space between the lines) increases, but the text itself remains unchanged. The labels on the player controls do get larger, but they both overlap and underlap the slide, making them unreadable.

Images for reference:

Making matters worse, accessibility extensions (including Helperbird, as shown in the support article's demonstration) also have no effect on the text. Here are images illustrating that problem as well:

In my Storyline project, I have:

1. Upgraded the project text
2. Set the course to display accessible text by default
3. Set the text box autofit options to "Fixed Size" and "Add Scroll Bars"

Guidance here would be appreciated. I have attached the Storyline file for inspection. 

Thanks!