I guess let's start here if have updated drivers: Try disabling uBlock Origin 1.13.0 and see if things work.

As I stated, safe mode did not resolve issue. I tested with uBlock disabled and no joy. It seems that some sources are more prone to go low than others e.g. Glow, on Netflix seems less cooperative than Monster Fish. Perhaps my tastes are too eclectic? :)

There are 3 things to check. First is the volume control of the computer. Check for new drivers or if old ones corrupted.

2, run MS Powershell or MS Dos prompt as a administrator and type sfc (space) /scannow sfc /scannow and see if there is any windows issues.

The 3, is the volume control in the video window.

Many site issues can be caused by corrupt cookies or cache.

   Clear the Cache and 

   Remove Cookies Warning ! ! This will log you out of sites you're logged in to. 

Type about:preferences<Enter> in the address bar.

   Cookies; Select Privacy. Under History, select Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.
   Cache; Select Advanced > Network. Across from Cached Web Content, Press Clear Now. 

If there is still a problem, Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences<Enter> in the address bar

Select Advanced > General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites. Are there any problems?

Then restart.

Please let us know if this solved your issue or if need further assistance.

I failed to mention I did all of that before posting to the forum. Besides, if we know that restarting Firefox resolves problem temporarily and the above does not, then isn't that a clue? The only things changed were the 2 driver sets. It seems that Firefox isn't playing nice with new drivers.

That is always a possibility that the drivers were not tested for ver 54 before release. Is there any harm in going back till their next release ?

Could also be flash that is corrupted.

Or stick around and am sure maybe someone else can help you out further.

I think it's likely that testing was neglected. I won't go back to previous version because the new drivers are better. Flash is not involved. I have it set to, ask, and 99% of my video viewing is HTML5.

I've been using Firefox since the '90s, so I guess I like it. I don't agree with the rollback mindset. I worked for Wall Data in the '90s and they were making bank with integration software. They attracted and maintained a large customer base by being willing and able to write, test & push working patches within hours. Those were the days :]

Anyway, I will likely become a 2-browser guy until Firefox is better. Google really wants me to try Chrome...

I bet they do, give more data ...

Just hang in here, someone with more experience or a better idea will get to you as they can.