SeaMonkey URLBarJS behavior change.
(Not sure when exactly, or why, but...)
viewtopic.php?p=69847#p69847> noscript.allowURLBarJS -> true
In SeaMonkey, you don't even need to do that.
All you need to do is to open about:config. That is sufficient.
Then just type your data: URI (or javascript: code).
Above is how it used to be.
Now you do have to actually set the Pref to 'true'.
I actually found the old way mighty convenient (though less secure).