I need a script or app to scroll all the way to the bottom of a verified account's /followers page on Twitter. There are millions of followers which makes automation a necessity. What are the options other than auto-scrolling apps that are understandably too slow for this?
There are Chrome extensions like Autoscroll which will endlessly scroll down the followers page all the way to the bottom, however, after a dozen of thousands or so of accounts scrolled, the page becomes too heavy for Chrome to handle and Chrome will eventually crash.
The proper way of doing this will require you to write code. Nevertheless, if the user of interest has indeed millions of followers, even writing code is not enough because Twitter's free API (code) access is rate limited and it may take days or even weeks to complete (it takes about 46 hours to download 500K followers using the free API).
Twitter offers a Premium API with lesser limitations but this is an expensive service that is not designed for a one shot.