Ajax functionality gone after RC4

Upgrading from rc3 to rc4 made all the ajax functionality go away. I used the jstools collapsibleblocks module, and I noticed it stopped working. So I uninstalled that in case it interfered with the new core. But I also see that I can't click and expand the menu headings on admin/settings or formatting options when submitting content (or other expandable headings). It's the same whichever theme I choose too. I use firefox 1.5 but it's the same in IE and Opera.

My enabled modules are listed under. I have tested enabling and disabling but can't figure out which is not compatible with rc4 ! Can anyone please review and help ?

actions
aggregator2
aggregator2_logo
block
blog
blogapi
buddylist
captcha
comment
contact
content
customerror
dashboard
date
filter
flickrstickr
forum
image
img_assist
invite
locale
logintoboggan
mailalias
mailhandler
masquerade
menu
node
nodereference
number
og
og_block
og_views
optionwidgets
page
path
pathauto
profile
robotstxt
search
securesite
story
system
taxonomy
taxonomy_context
text
textimage
throttle
tinymce
user
user_status
userreference
views
views_ui
voting_actions
votingapi
watchdog
weburl
workflow