User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:34.0) Gecko/20100101 Firefox/34.0 (Beta/Release) Build ID: 20140722030201 Steps to reproduce: 1. Set up a proxy in Advance Settings -> Connection Settings -> Configure Proxies to Access the Internet, by setting the Automatic proxy configuration URL to appropriate value. 2. Setup multiple home pages, so multiple tabs are opened when Firefox starts afresh 3. After all tabs have loaded, open a new tab with Google as home page Actual results: "Unable to find the proxy server" error appears instead of loading the home page. Entering an address in URL bar yields the same error message. If you enter e.g. https://bugzilla.mozilla.org in the URL bar, same error message appears. Now if you close Firefox and open it again, (if restore tabs is enabled) https://bugzilla.mozilla.org tab loads just fine. Seems like newly opened tabs does not get proxy correctly Expected results: With proxy set correctly, when a new tab is opened, it should load correctly. This only started happening in this week, proxy was working fine in the last many months.

I suspect bug 354493, but a proper regression window would help (if you have time/energy, using http://mozilla.github.io/mozregression/ to track this down would be very helpful!). Can you check if this is fixed if you use a build from http://ftp.mozilla.org/pub/mozilla.org/firefox/try-builds/sworkman@mozilla.com-8e3a63e3afd7/try-win32/ (which contains the patch from bug 1041511 which fixes some proxy-on-localhost-related issues) ?

The try-build seems to fix the issue. I will try to get a regression window and get back here.

(In reply to Mahesh Asolkar from comment #2) > The try-build seems to fix the issue. In that case, this is effectively a duplicate, I believe. :-)