I try on the desktop, and it works! Well, I don't have a key, but the alert fires as least.
Does Android require signed packages for JS to run, or what am I missing here?
The fact that there is no way to get the sync key out of FF for android NOR export bookmarks is, to use a strong word, retarded. Googling around there are many many threads from people who have, like me, lost their recovery key. It's aggravating because the data is there. I have my bookmarks on the device. I know the key is in there or it couldn't decode them. There's just no way to get at it because everything is locked down.
The JS looks like this (oh great, no preview here. How nice):
One thread suggested 'jailbreaking' and then somehow exporting the sql-lite(?) database containing the key, extracting it from there. I'm not doing that. This isn't supposed to be hard, this is supposed to be three clicks and you're done.
For the love of all that is holy, someone add Export Bookmarks to the Android version so we can get on with our lives.