Mozilla VPN desktop cannot log in when vpn.mozilla.org pages are prevented from making cross site requests to localhost loopback 127.0.0.1

[turbocrime]

when attempting login to Mozilla VPN on a new desktop device, logging in successfully in my browser did not change state within the Mozilla VPN app, which continued "waiting for sign-in".

versions

• mozillavpn 2.29.0 (2.202506162352)
• macos sequoia 15.5
• firefox 141.0.3 (aarch64)

solution

to fix this, i temporarily disabled my ad blocker for vpn.mozilla.org to complete login.

cause

i use ublock origin and i had enabled the "block outsider intrusion into lan" filter set.

apparently, the mozilla VPN login makes a cross-domain request to localhost at 127.0.0.1, and was interrupted by this filter.

maybe Mozilla VPN should not rely on a cross-domain request to log in

i think it is generally not a great pattern, and also, many people will be running filter lists or blocking this kind of request for security reasons and privacy reasons and by default someday

not solutions

i am posting this github issue so that my particular cause and solution is documented somewhere.

annoyingly, lots of discussion contained little information and few suggestions other than 'contact support, the solution they give you is easy'

clearly similar issues may happen for several reasons, and vary depending on platform and version.

github issues that did not help (but at least made it clear that the causes could be various)

• Error "waiting for sign in and subscription confirmation" when logging in. #965
• VPN version 2.7 - Error "Waiting for sign in and subscription confirmation" #2830
• Unable to complete VPN authentication on iOS #2906

mozilla support questions with an accepted answer containing no information:

• https://support.mozilla.org/en-US/questions/1305793
• https://support.mozilla.org/en-US/questions/1342760

mozilla support articles that were not helpful

• https://support.mozilla.org/en-US/kb/i-cant-sign-mozilla-vpn-what-should-i-do
• https://support.mozilla.org/en-US/kb/how-log-mozilla-vpn

reddit threads with no solutions

• https://www.reddit.com/r/firefox/comments/pb9rjb/how_do_i_use_mozilla_vpn/
• https://www.reddit.com/r/firefox/comments/imt68g/logging_in_to_set_up_mozilla_vpn_on_windows_10/

[oskirby]

Thank you for the detailed analysis, and I agree that this is a poor design decision on our part. The use of localhost for the login procedure has become a high priority issue to fix in light of the recent security issues (and due to upcoming changes in Firefox that make it much harder to access localhost). We are working on fixing this and hope to have an update soon that will switch to using deep links for web-based authentication flows.

Internally, we tracking this issue as VPN-7211