Firefox 99 started serving a "What's New" page that is an ad for Pocket instead of listing what's new in the browser.

Another disappointment.

Here's how to disable the now useless "What's new page":

1. Go to about:config

2. Change the value of "browser.startup.homepage_override.mstone" to "ignore".

Bingo! One less page with ads.

Thanks for nothing, Mozilla.