at an add-ons hackday event, the network was kicking people off shortly after they joined. this allowed them to log into builder, but then the network would die while they were mid-way through their hello-world example. so they'd hit save or test, and nothing would happen. the save button would stay red, the test button would not stay depressed, etc. the user was not notified that the problem was that the builder server could not be connected to! the builder should disable basically everything when it can't connect to the server, and communicate that clearly to the user.
The builder project has been discontinued as of April 1st, 2014. The announcement last year: https://blog.mozilla.org/addons/2013/12/18/add-on-builder/ Next steps (still being written): https://developer.mozilla.org/en-US/Add-ons/SDK/Builder