First of all: Thank you for helping us getting to a stable release build by using the development build.
Terryphi wrote:When Firefox 57 is released, and presumably the stable version of AdblockPlus is released, will the development build automatically update to the release build?
No, our development builds are updated in parallel with our release builds so you can, for instance, run both side-by-side. Both the development build as well as the release build of our current Firefox extension will be automatically updated to the new web extension version as soon as they're ready.
So what you can do is either continue using the development build to always have the latest version of the extension or switch to the release build before or after the new version has been published.