User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:55.0) Gecko/20100101 Firefox/55.0 Build ID: 20170612224034 Steps to reproduce: I attempted to cast unrelated apps on my home network to Google Chromecast audio and video units. Actual results: My phone failed to discover most of the Chromecast-enabled devices on my network in both Google Home or Spotify's Spotify Connect screen, until I killed Firefox for Android on my phone. Setting 'network.mdns.use_js_fallback' to `false` appears to help too, as mentioned in https://bugzilla.mozilla.org/show_bug.cgi?id=1347755. Expected results: All devices should be immediately discoverable in apps that can initiate Chromecast sessions. While I'm not positive Firefox for Android is the culprit, I suspect this is the case based on my experience when I dealt with bug 1347755 and in the way it seems to recover in the two ways mentioned above. This seems particularly insidious because there's little reason to connect the Chromecast failure to Firefox for Android. So this issue may be highly underreported.

Changing the component to Screencasting, if anyone feels like this is not the right component please feel free to change it back.

The only point I'd make is that I've never attempted to cast from Firefox, it just seems to interfere with casting from other apps and my network in general. But whatever works!

Hi James: if this something related to your fix in https://bugzilla.mozilla.org/show_bug.cgi?id=1347755? Would you kindly check? Thanks.

Can't hurt to set network.mdns.use_js_fallback to false everywhere. We only did it for release earlier because we thought FxOS presentation support was the problem, which is disabled in 53 I believe. Flipping the pref will make sure the problematic JS fallback isn't used anywhere.

Comment on attachment 8883565 [details] Bug 1374647 - Disable mDNS JS fallback in Fennec https://reviewboard.mozilla.org/r/154502/#review159584

Pushed by jwillcox@mozilla.com: https://hg.mozilla.org/integration/mozilla-inbound/rev/f4406d351311 Disable mDNS JS fallback in Fennec r=esawin

Comment on attachment 8883565 [details] Bug 1374647 - Disable mDNS JS fallback in Fennec Approval Request Comment [Feature/Bug causing the regression]: Unknown [User impact if declined]: Bad network interaction, possibly hangs in Gecko [Is this code covered by automated tests?]: No [Has the fix been verified in Nightly?]: No, but we shipped this same patch in 53 [Needs manual test from QE? If yes, steps to reproduce]: No [List of other uplifts needed for the feature/fix]: None [Is the change risky?]: No [Why is the change risky/not risky?]: Turns of busted JS fallback for mDNS and uses the platform implementation instead. [String changes made/needed]: None

Comment on attachment 8883565 [details] Bug 1374647 - Disable mDNS JS fallback in Fennec fix a bad interaction with chromecast, beta55+