I just got this to work late last night, and in Firefox
even!

The trick is to leave the browser tab open showing the
error message about the unsopported browser. From start
to finish, here are the steps:

1) Open the "standard" Harmony login page: [Link: members.harmonyremote.com]

2) Login using your user ID and password for the TC30.

3) You WANT to see an error message about using an unsupported
browser. If you get this error, do NOT click NEXT on
but instead proceed to step 4.

If you did NOT get the error message, but instead get
redirected to the Harman Kardon login page, go to Tools
> Options > View Cookies. Enter "members.harmony" in
the search field and remove the cookies from the members.harmony
site. Try Steps 1 to 3 again.

4) Click this next link to open the TestDrive site in
a new tab: [Link: members.harmonyremote.com]

5) You should immediately see your devices and activities
for the TC30 within the the "traditional" Logitech Harmony
web interface.

6) Have fun!

I have to say - what a pleasure it is to use the "tradtional"
interface again, especially since I can again use the
Firefox mod that allows soft-keys to be moved up and down!