Why you can't play 1080p or 480p YouTube HTML5 videos in Firefox anymore

The popular video hosting and streaming website YouTube uses two technologies to stream videos to its users. Either by making use of Adobe Flash, or HTML5 Video, with the latter option marked as experimental for some time now.
Provided that you have a HTML5 capable browser, you can join the HTML5 trial on YouTube to use this technology on the site. The core benefit here is that you do not have to install or use Adobe Flash Player at all.
To do so, load this page on YouTube http://www.youtube.com/html5 and click on the join button on it.
If you have not visited that page for a while, you may notice that Google has added three new bits of information to it. The page not only informs you if your browser supports HTML5 Video, H.264 and WebM VP8, but also if it supports Media Source Extensions.
If you open that page in Firefox, Safari or older browser versions, then you will notice that the browser's don't support it.

Media Source Extensions explained
The feature, in layman terms, allows web applications such as YouTube or Netflix to generate media streams for playback in JavaScript. This makes way for new features such as adaptive streaming (for instance MPEG-DASH) or live streams, or to transfer encrypted contents to the user, decode it using JavaScript, to play it in the browser afterwards.
A highly technical draft document is available here that provides you with additional information about Media Source Extensions.
YouTube

If you are using the HTML5 video player on YouTube in Firefox, you may have noticed that you do not get to select 1080p or 480p as the video resolution no matter what you do.

You may have also noticed that you do get to select 1080p if you leave the HTML5 beta and return to Adobe Flash Player.
Google recently switched to adaptive streaming on YouTube for 480p and 1080p videos by using Media Source Extensions. Since Firefox does not support that feature yet, the option to switch to streams that make use of it becomes unavailable in the browser.
That's why you cannot select 1080p or 480p anymore if you are using Firefox and have joined the HTML5 video trial.
The only way around this for now is to use Adobe Flash to play videos on YouTube.
Mozilla
Mozilla is working on an implementation of Media Source Extensions, but it is not clear yet when it will become available. You can follow these two bugs on Bugzilla to monitor the progress made in this regard.
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thanks you saved my 1000 tabs :)
Fantastic! Thank you! This worked like a charm. Had exactly the same issue in Firefox on a PC and this fixed it.
Thank you for sharing this! Like you, I’d noticed that disabling/re-enabling the extension would work for that browser session, but I hadn’t tried anything yet to force a fix. I’m SO glad it was this easy!
I sure hope the OneTab team issues an official fix ASAP, though. Now that it’s been a few days, they’re starting to get bad reviews, which is unfortunate.
Yes! I also tried the workaround. I also reported this bug to OneTab team on the first day I faced this issue.
Thanks, Ashwin for the fix!
I was nearing desperation when I found your direction. It worked.
Thank you so much.
Hi, OneTab developer here. Sorry for this – it’s not clear why this bug is suddenly happening for some people, but we’re urgently investigating this with the Mozilla/Firefox team and will be providing a fix very shortly.
Thank you so much for sharing this fix! You saved my tabs. The only note/point I would like to add is for Step 2.
Perhaps put a note stating they should copy Step 3 and forward of your tutorial to Word. Once we close Firefox, we lose visibility to your tutorial. For me, I know I would not be able to remember the .bkp.
Again, thank you!
Easy temporary fix: To make OneTab work again, type “about:addons” in your Firefox address bar. Then find OneTab in the list of extensions, and click the blue toggle button twice. This will disable and then re-enable OneTab, and cause it to work again.
We’re working with Mozilla for a permanent fix. Sorry for the inconvenience, this is a very strange issue that is only affecting the Firefox version of OneTab.
I have found by disabling and then re-enable in the add on menu I get my tab back. Short term fix. Will try yours.
Thank you. I thought I had lost a month of digging. I’ll be a little more attentive about exporting the urls from the extension list now. It’s a great tool but Firefox doesn’t always play nice with its extensions.
Good news – I’ve been working with Mozilla all morning to resolve this. Mozilla have confirmed it was due to a bug in Firefox (related to extension permissions downgrades).
To fix OneTab, just go to “about:addons” in your Firefox address bar, click the ‘cog’ icon in the top right, and click ‘Check for updates’. This will upgrade you to OneTab v1.39, which fixes the issue.
Darn, I tried everything here and I still can’t get my tabs back. I even did a full system restore to a point last week hoping that my saved tabs would be in the old .xpi file, but no luck.
I’m pretty disappointed :(
Probably I should’ve been more patient, but now I don’t know how to feel about this. I lost about 900 tabs in the recovery process (I reinstalled OneTab), which, incredible as it sounds, weren’t all just a messy dump I’m never going back to, but actually important stuff (yeah, I have a peculiar workflow).
Trying to suppress the anger and reflecting on what happened, it seems I should blame myself for not having a backup. But surely I couldn’t back it up manually every time I save a tab, it would defy all purpose of having this addon in the first place. A couple of years ago data was stored at “~/.mozilla/firefox/%PROFILE%/jetpack/[email protected]/simple-storage”, and you could back it up with simple crontab. This is no longer the case, this folder is just empty. And since OneTab is closed-source black box, I couldn’t have done anything else as well.
So the only reasonable lesson to be learned is that I actually must stop relying on OneTab, since sooner or later it will let me down again. Fuck it.
I just disable and re-enable. No tabs lost!
I switched from OneTab to Tab Stash (https://addons.mozilla.org/en-US/firefox/addon/tab-stash/) months ago and haven’t looked back. I had never experienced any data loss with OneTab, although I was a bit concerned by some reports of data loss I read about. My main issue was with OneTabs performance, it’s a hog. I had been looking for a replacement and testing out a ton of addons for a couple of months when I finally discovered Tab Stash, and am damn glad I did. I really can’t recommend it strongly enough…
Thanks, bsdaddict. Never tried it, looks nice, but I’m a bit concerned by small number of stashed tabs on these screenshots, not sure if it’d be usable when stashing a lot of tabs. How many tabs do you usually have stashed?
Tab Stash is is a great alternative to One Tab, y’all… I made the switch months ago and am very happy with it.
>DO THIS FIRST: Before trying the following fix, I recommend disabling OneTab and re-enabling it from the about:addons page, to access and regain your tabs.
Worked for me! Many, many thanks!
I know it’s late but ist there an option for chrome on android tablets aswell? My wife hates it that the search bar and Tab list will just come Up again when she Scrolls up
You are truly a hero and a scholar, sir or madam. I salute you!