I just decided it was time to list Rhapsode alongside Lynx, Dillo, and NetSurf as a smaller engine you can help grow by making sure your pages look (or in Rhapsode's case, sounds) decent in them.
But definitely, test in Firefox and Safari/Midori/GNOME Web/Odysseus/etc too! Whatever you do don't just test your pages in Chrome, I fear a Google monopoly.
Here's my other asks: https://odysseus.adrian.geek.nz/developer/web-bloat.html
In Rhapsode's case specifically, you should be:
1. Writing semantic (X)HTML5
2. Declaring your page's language
4. Avoiding excess text
5. Making sure your site's fully navigatable without it's navbar
Though you can go further if you want: https://git.nzoss.org.nz/alcinnz/rhapsode/wikis/CSS-Speech-Tutorial
This helps Rhapsode to give it's most engaging monologue, whilst allowing your readers (once I implement the vital feature) to navigate your site.
I find Firefox is the best for testing anyways. Chrome has the better dev tools, but Firefox handles caching slightly better.