If Firefox's developers are worried about people not understanding why a page doesn't work, another potential solution would be to provide users with some feedback. For instance, if Javascript is disabled but present in a page, perhaps show a (simplified?) small debugger box showing the next lines of Javascript which would have been executed and some sort of an obvious Run / Play button to start the script.
I'd prefer if browsers treated the Web as less of a black box, and if they erred more toward helping users understand the world they are exploring.
This is a great idea, but should probably be simpler for the average user. Eg "You have JS off, which will break some websites. Click here to turn it on. The simple option you used in the past to toggle this has gone. Click here to find out how to toggle it now"
I'd prefer if browsers treated the Web as less of a black box, and if they erred more toward helping users understand the world they are exploring.