I done that and have no problem with stopping the video and going to different points on the video. I got W10 MSI GTX1060 6G 16gig Soundblaster ex card. So I think your has to do with how your system is configure that caused this more then a FF issue.

Starting/Stopping/Jumping was not the issue. The audioeffects of my Sound Card do not take any effect after these actions.

Keep in mind that you will only be able to reproduce it, if you have any effects on the sound card, like the equalizer, active.

I've kept mine at default settings with Sound Ambiance as the only change and my youtube has no issue from FF56 to FF58. I still think something went wrong with the drivers.

Hi wengaCH, Let's try something simple, like clearing your cache and cookies.

1. Click the Library button and choose History.
2. In the History menu, choose "Clear Recent History...".
3. Under "Time range to clear", select "Everything".
4. Now, click the arrow next to Details to toggle the Details list active.
5. From the details list, check Cache and Cookies and uncheck everything else.
6. Now click the "Clear Now" button.

Chris Ilias said

Hi wengaCH, Let's try something simple, like clearing your cache and cookies.

1. Click the Library button and choose History.
2. In the History menu, choose "Clear Recent History...".
3. Under "Time range to clear", select "Everything".
4. Now, click the arrow next to Details to toggle the Details list active.
5. From the details list, check Cache and Cookies and uncheck everything else.
6. Now click the "Clear Now" button.

Did all of that, cleared all of the cache, cookies, settings and history. Yet it did not help. I can still reproduce the sound issue.

Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

• Click the menu button , click Help and select Restart with Add-ons Disabled.

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

Chris Ilias said

Try Firefox Safe Mode to see if the problem goes away. (...)

Hi Chris. Just did that. I can still reproduce the issue. So no add-ons are affecting it.

Let's try resetting Firefox: Reset Firefox preferences to troubleshoot and fix problems

Chris Ilias said

Let's try resetting Firefox: Reset Firefox preferences to troubleshoot and fix problems

Did not fix the problem.

Update:

Can be reproduced on Vimeo as well. So it's probably a HTML5 media issue

Unless someone else has another suggestion, the only other thing I can think of is to make sure your drivers are up to date. If they are up to date, it looks like a bug. :(

So I finally managed to update all drivers and the system itself. It did not fix the issue, but it seems, that Firefox is not the problem. I was able to reproduce it in IE Edge on Netflix. Seems like Windows 10 hast issues with HTML5 streams in certain situations.

Thanks for letting us know. :)