It's currently impossible to recover a password and then login on this site, it results in a redirect loop, this is the error message you get in chrome (which is clearer than the firefox one):
The webpage at http://dev.piwik.org/trac/prefs/account has
resulted in too many redirects. Clearing your cookies for this
site or allowing third-party cookies may fix the problem. If not,
it is possibly a server configuration issue and not a problem
with your computer.
Clearing the cookies for the site doesn't help.
To reproduce this error, request a password reset and then try to login with the password sent by email.
I got around this bug by creating a new account...
IIRC this is a trac bug, fixed in newer versions. Should we upgrade to 0.11.7, or jump to 0.12.x ?
We have finally upgraded Trac to the latest version and now Login + Reset password should work for all users. Please let us know if you have any problem with http://dev.piwik.org