Firefox 57 drops support for all legacy add-ons, including
Tab Mix Plus. From Firefox 57 onwards, Firefox will not install
Tab Mix Plus.
I am currently working on converting Tab Mix Plus code base to the new WebExtension format.
Tab mix code base holds more than 35,000 line of code in 139 files.
It is currently unclear when Tab Mix Plus as a WebExtension will be ready, it will not be ready before Firefox 57 official release. I am also not sure it will be possible to implement all Tab mix features in the new format.
Anyone who wants to contribute code or assist in any other way can contact me directly via email@example.com.