Good news: All issues are resolved and the RPA software is available for Firefox again:
UI.Vision RPA – Get this Extension for 🦊 Firefox (en-US) 
The new version number is V5.89, but it is exactly the same as V5.88. The version number bump is only for admin reason.
I want to use this occasion to thank the Firefox team you for making sure that the content of the Firefox add-on store remains reliable, secure and of high-quality. This benefits all Firefox users, and also all the honest add-on developers.