Why do developers need to "update" their software by going backward ? I'm going back to the 2.9.1 version :(

Update
Here's the link to old versions (forget 2.99)
https://addons.mozilla.org/fr/firefox/addon/adblock-plus/versions/beta?page=3#version-2.9.1.4260-beta
It will stop working with Firefox 57 https://adblockplus.org/development-builds/
I'm sick about softwares like Firefox that where poorly designed in a way that they have to rewrite part of their stuff which for a software that use plugins made by others is just wrong.