I watch Youtube on html5 with Iceweasel browser on Debian 8.
Just a few days ago, Youtube said my browser was no longer supported and I should install Firefox or Google Chrome.

So I then upgraded the Debian OS with 'apt-get update' and then 'apt-get upgrade' on the root terminal.
Whilst the OS was upgrading, it told me that it would now use the NEW Mozilla Firefox certification.

I thought that this meant that Youtube would now continue accepting my Iceweasel browser as Firefox (which it mostly is).
However, despite a successful upgrade of Debian 8 where the new Mozilla certification was installed, Youtube is still saying my browser is unsupported!
I can watch videos but I can't write comments any more. This makes Youtube useless for me.

Can anyone please say how I can still use Iceweasel with Youtube, or if I really do need to install Firefox?

are you sure you're using html5 instead of flash?

from what i see, this is more likely to be your situation:
it is caused by adobe's abysmal support for linux platform (we're still on version 11, while the rest of the world is at 19 or 20) - at some point mozilla (firefox/iceweasel) decided to throw a warning about it being insecure (i do not use flash, i'm quoting this back from other forum posts).

have you tried simply uninstalling flashplugin?

edit:
i think your comment problem is unrelated.

Thank you for your reply. I don't have Flash installed on the Debian OS and can only watch Youtube on html5.

My difficulty is that I've installed the new Firefox certification onto Iceweasel (from the Debian repos), but Youtube still does not seem to accept this.

What version of iceweasel are you running?

ok, sorry about that.
i have a debian stable system with iceweasel 38.6.0 running and i cannot reproduce.
i do, however, not login to youtube.

i cannot find that "certification" anywhere on that debian system.

i'm not sure i understand the nature of the problem, but could you try a useragent spoofer addon, and spoof it to windows firefox or some such?

You could install the backports version. It's compiled from the newest Firefox sources (here: http://mozilla.debian.net/).

installing firefox on Debian is not big a of .. hard thing to do, it was one of the first things I did when I was using debian.

then just hack pepperflash into a dummy directory structure that mimmics Chromes then you're back on track...

Iceweasel browser is showing me I have version 31.3.0.

I thought Iceweasel automatically updated itself.
So if I have an old version of Iceweasel, then perhaps updating might solve the problem.
However, how do I update Iceweasel?

Yes, Youtube will send the message that the browser is no longer supported once you've logged in.

That's unusual. Before the upgrade was installed on my system, I saw a message on the terminal saying that the Mozilla certification would be installed.
Maybe it's because I have Iceweasel 31.3.0, but I'm not sure.

What is the backports version of Iceweasel?

Also, will I need to uninstall the stock Iceweasel on Debian 8, or won't that be necessary?

Ah yes. Well, Youtube is Google - the spymaster general himself. So I want to avoid mimicking Chrome in case Google finds out and kicks me out of Youtube!

all you're doing is creating a dummy/empty dir structure and putting pepperflash in the dir that is in the path that youtube and other sights look when seeking out a flash plugin is all... did someone say paranoid?

Thank you. I was really hoping to continue using Iceweasel browser and playing videos on html5.

I think I have an old version of Iceweasel and updating to the latest version may mean Youtube sees Iceweasel as Firefox.
On the 'Preferences, Advanced, Update' tabs of Iceweasel, I only have the option to automatically update search engines. There is no option to automatically update the browser.
This is weird because I think Firefox has the 'update browser' option.

Correct, that is one of the few differences between iceweasel and firefox. Iceweasel (because it's in the repositories) has the autoupdate removed.

Also, just went on youtube on a virtual machine with Debian stable, and no issues with youtube with no flash of any form installed, even after logging in.

What is the Iceweasel version you're using? Mine is 13.3.0.