force_auth does not login properly, stuck on Working...

[vladikoff]

context: fx_desktop_v2
firefox: 45.0.2

happens both in prod and local dev

STR

• sign in with an account to Firefox
• open a new tab and go to /clear to clear storage
• go back to about:preferences#sync
• click "Manage Account"
• try to signin in the new tab (with the session expired warning)

Expected

Should login

Actual

The UI is stuck on Working....

GIF

[vladikoff]

Can be testing locally with:

Prod:

➜  fxa-local-dev git:(master) pwd
/Users/vladikoff/mozilla/fxa-local-dev
➜  fxa-local-dev git:(master) FXA_ENV=prod npm start

Local (have servers running):

➜  fxa-local-dev git:(master) npm start

[shane-tomlinson]

Dup of #3603, same root cause.