Firefox 24 uses stale manual proxy settings when configured to use system proxy settings, and system proxy settings are set to "None"

[Budo Zindovic]

This problem is the same as the one reported for Firefox 22 (https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1194841). The workaround mentioned there still works. While this problem is resolved for the previous versions, current version of Firefox is plagued by this bug.

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ProblemType: Bug
DistroRelease: Ubuntu 12.04.3
Package: firefox 24.0+build1-0ubuntu0.12.04.1
Uname: 3.8.0-30-generic
AddonCompatCheckDisabled: False
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.25.
ApportVersion: 2.0.1-0ubuntu17.4
Architecture: amd64

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Wojtek Kazimierczak (w-kazimierczak)]

Same problem with stale manual proxy settings in 25.0+build3-0ubuntu0.12.04.1.
Workaround works.

[Marian Hello (marian-hello)]

Still valid in Ubuntu 16.04.1

How to reproduce (set some invalid host and port

gsettings set org.gnome.system.proxy mode 'manual'
gsettings set org.gnome.system.proxy.http host 'nonexistinghost'
gsettings set org.gnome.system.proxy.http port 9999
gsettings set org.gnome.system.proxy mode 'none'

Expected outcome: FF will not use any proxy and any website will be normally accessible.
Actual outcome: Visiting any page result in: The proxy server is refusing connections

[Marian Hello (marian-hello)]

Workaround for Ubuntu 16.04.1 and Firefox 49.0+build4-0ubuntu0.16.04.1:

gsettings set org.gnome.system.proxy mode 'manual'
gsettings set org.gnome.system.proxy.http host ''
gsettings set org.gnome.system.proxy.http port 0