User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:54.0) Gecko/20100101 Firefox/54.0 Build ID: 20170511130324 Steps to reproduce: Starting with the first or second most recent Firefox stable release (53), some of our users have reported that when using Firefox for a short while it will stop loading web pages. We use an NTLM authenticating proxy server so that accepts the users' logged in domain credentials. Actual results: No errors or prompts are displayed, not even a page timeout. The circular loading graphic on the tab spins as if the page is loading, but it never completes. All attempts to load any page in the current tab or another tab silently fail in this fashion until the user closes and opens Firefox again. I've had affected staff try the latest nightly build (55.0a1) but the consensus so far is that the problem still occurs. Expected results: Of course, the web page should load without having to kill the browser. This behavior has not been reported with Chrome or Internet Explorer, so I don't know if those browsers have more robust handling of differing proxy behaviors or if this problem is exclusively Firefox's.

Please double/triple check this is not duplicate of bug 1360574. The symptoms are quite the same. The fix has landed on 2017-05-14 on mozilla-central (Nightly). Note that we stopped updated to Nightly just yesterday for some different bug. Please wait until a Nightly release containing https://hg.mozilla.org/mozilla-central/rev/9051132444a0 is out.

That bug was brought up when I first mentioned this issue in bug 1351462, but I wasn't given enough information to pursue that possibility (about:networking didn't reflect having hundreds of connections open, and didn't indicate how many connections had been made that browser session). Comment 40 (https://bugzilla.mozilla.org/show_bug.cgi?id=1360574#c40) indicates that the bug may be fixed in the latest beta release. Should I have affected users try that or wait for a nightly as you suggest?

(In reply to raynebc from comment #2) > That bug was brought up when I first mentioned this issue in bug 1351462, > but I wasn't given enough information to pursue that possibility > (about:networking didn't reflect having hundreds of connections open, and > didn't indicate how many connections had been made that browser session). > > Comment 40 (https://bugzilla.mozilla.org/show_bug.cgi?id=1360574#c40) > indicates that the bug may be fixed in the latest beta release. Should I > have affected users try that or wait for a nightly as you suggest? I think you can check with Beta, yes. Note that switching between Release/Beta and Nightly while using the same profile might be a bit risky (some profile data could get broken, specially these days). So, try to minimize taking people from Release to Nightly and then back or to Beta unnecessarily. Some isolated testing should be enough to confirm this.

Even if the profile was broken, Firefox still regularly backs up the user's bookmarks by default, right?

Reopen the bug if you can reproduce the problem with the version mentioned in comment #1.

The multiple users that reported this problem indicate that is stopped happening with the latest beta releases. I think we can consider it fixed.