[perihelions]

- "Now I'm figuring out how to disable notifications that an update is available and prevent checking for them entirely so that I don't get shown an ad because I made the mistake of updating a piece of software."

I haven't tested it, but this page describes an about:config flag that apparently inhibits the /whatsnew/ page:

https://kb.mozillazine.org/Startup.homepage_override_url

    If browser.startup.homepage_override.mstone is set to "ignore", the browser's homepage will not be overridden after updates.