>>> My Info: Win7_64, Nightly 53, 32bit, ID 20161119030204 (2016-11-19) STR_1: 1. Open new tab (or about:preferences) 2. Paste url [1] into urlbar, press Enter 3. While page is still loading, click play button in the 1st comment (if you failed, goto Step 1) 4. Wait until the page loads, then wait 5 seconds, stop the video > [1] http://funnyjunk.com/Tumblr+twiiter+comp+7/funny-pictures/5849578/24#24 AR: Step 3 - the video doesn't start. Tab displays "play" button. Step 4 - the video starts playing ER: Step 3 - the video should start playing; no need for blocking media, because it's selected tab STR_2: (reference of good behavior) 1. Open http://example.org/ 2. Paste url [1] into urlbar, press Enter 3. While page is still loading, click play button in the 1st comment (if you failed, goto Step 1) AR: Step 3 - the video starts playing, just as expected Note: "regressionwindow-wanted" means that in this bug it's necessary to find bug where the feature was implemented in broken state. First check bug 1308153 - it can save some time.

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:53.0) Gecko/20100101 Firefox/53.0 I have tested this issue on Windows 7 x64 and Windows 10 x64 with the latest Firefox release (50.1.0), the latest Nightly (53.0a1-20170102030204) and with the build specified in the description and also with older nightly builds(23.0a1, 24.0a1,28.0a1,29.0a1, 49.0a1) and haven't managed to reproduce it. After opening the about:preferences tab and pasting the url [1], while still loading the page, when clicking the play button in the 1st comment the video starts playing. When following the steps in STR_1 the AR are the same as when following the STR_2. I have tested this on issue on high end machines with great internet connection. Could this be related to one of these factors? Do you have a lower end machine or bad Internet service?

>>> My Info: Win7_64, Nightly 53, 32bit, ID 20161229030206 (2016-12-29) Reproducible with advice (1) below. Not reproducible w/o it, it seems... > I have tested this on issue on high end machines with great internet connection. > Do you have a lower end machine or bad Internet service? I don't know how to make it reliable then. I sure can't describe my internet connection as "great" at all, even though it's claimed to be "100Mb/s". Well, I have some ideas. Please try these and respond: 1) Replace Step 1 to "1. Open about:preferences, close other FF tabs and FF windows to kill child processes" 2) Replace Step 3 to "3. While page is still loading, keep hovering the video and moving mouse away from the video, until you see the purple text 'The video will start after 1 second' above the video. When you see the text, keep mouse above the video. The described process will trigger the page to start the video automatically. Ofc step will fail if the page loads too fast" This replacement is only required if you're unsure whether click in original Step 3 triggered the page to play the video, i.e. specific script is loaded (yes, the page overrides your click). 3) Try slower internet connection. Not really sensible advice, since I personally don't know how to do that. But it seems that the new Responsive Design Mode is able to do that. I remind you that the bug is that playback of video is blocked before (apparently) 'load' event. Also, add "[e10s]" in the beginning of the summary, once it's confirmed that it's e10s-specific bug. [OOT] > I have tested this on issue on high end machines with great internet connection Why would you do that? I usually say informally that FF developers use the best/latest PCs with perfect internet connection to avoid FF issues, it appears I was right all along(?!). Please use some machines / internet connection from real life fgs.

After re-testing this on a lower-end machine, I was still unable to reproduce the issue. I will mark this as Resolved-Worksforme. If anyone can still reproduce it, feel free to reopen the issue and provide more information.

>>> My Info: Win7_64, Nightly 53, 32bit, ID 20170107030205 (2017-01-07) Reproducible, just as said in STR_1. There's also a short period when video actually starts playing - it doesn't produce any sound in the beginning, so tab still displays "Play" button. When video starts producing sound, "Play" button in tab is replaced with sound indicator.

After re-testing this on a lower-end machine, I was still unable to reproduce the issue. If anyone can still reproduce it, feel free to reopen the issue and provide more information.