Marking as solved! The solution is a tad cumbersome (can't directly control in-browser), but it comes with a bonus I didn't even think to ask for (mp3 files that I can save to my phone and listen to in the car!).

Using the extension Video Download Helper, I can yoink the sound files right off the website. I've got mp3's set to open with Firefox, so when I open one it launches in its own tab, where I can use the extension Video Speed Controller to manipulate the playback speed; click back to the original ATI tab and read along.

Thanks for the help, all!!!

[/edit]

Just started nursing school (fuck yeah!!) and it's looking like a lot of our material is via the website https://www.atitesting.com/ (couldn't find any examples of the audio feature that don't require you to be logged in).

It's basically a textbook, broken down into modules, and click through them as instructed. There's a "play audio" feature that provides audio of the wall of text, which is great! ...except that whoever made the recordings sounds like the fucking sloth from Zootopia.

Occasionally there're videos too, which also don't have built-in playback speed options, but I found an HTML5 video speed controller extension for Firefox that works a charm on those; I've tried about 10 similar extensions trying to hit the text audio, but it remains stuck on sloth.

I also tried a program called Cheat Engine - used that about 50,000 years ago to skip ads on YouTube when YouTube was first infected with its ad disease: set the runspeed of Firefox to like 100x and the ad would be finished in about half a second. Doesn't work anymore for ads, and didn't work on ATI's audio either.

Not sure what else to try, but there aren't enough hours in a day to listen to the assigned material at 1x, so if you've got a fix, you're my hero!

Thanks all!!