In TenFourFox, go to Tools and Add-ons, and make sure those
add-ons are enabled (Firefox 3.6 might not have enabled them).
However, you should not switch back and forth between Firefox and
TenFourFox -- pick one or the other. TenFourFox's configuration
files and add-on compatibility are now different enough from
Firefox that you can corrupt your profile if you're not careful,
which can cause both browsers to behave incorrectly. You may wish
to read some of the entries we have in the TenFourFox FAQ about
that. If you must run Firefox 3.6, it would be a good idea to
create a separate profile just for that purpose.