I had the same thing happen last night when I created a new profile
with one of the nightlies + some files from my old profile (which has
various Firefox 2 and extensions cruft). The "classic" bookmarklet
worked, but not the other two. Swapping back to my old profile fixed
it.
I had the same versions of these files in both profiles:
-GUI and website-tweaking CSS in the chrome folder
-adblockplus (folder with support files)
-cookies.sqlite (didn't want to log into several dozen sites again)
-places.sqlite
-signons.sqlite
-my user.js file, which has the following cookies & javascript prefs
set (again, also present in the working profile):
user_pref("network.cookie.cookieBehavior", 1); with
blinklist.com
added to the cookie exceptions list via Firefox's GUI in both profiles
and several prefs to enable the new JavaScript engine
so I'm also stumped as to what it is.