Here is a tiny test video, which shows the little Z80 SBC (Single Board Computer) running a "ripple pattern". Its the direct link.  You can use it to check if your HTML5 rendering is correct.

http://d3rd3i2xz0wkmj.cloudfront.net/89/67/vid--443811843-205281fb-bf82-4542-b33b-dc244e20dc81-640x360.mp4

(Now that Quirksmode has gone dark, figure we need a  quick HTML5 test/check thing!)

This is the Youtube page for HTML5 rendering test/verify.

Getting the various versions of Firefox to work correctly with video can be a chore.

The more recent versions almost work.  But various platform characteristics and requirements, often dictate that specific (older) versions of Firefox be used.

We run a mix of older boxes, with a variety of specialized software and hardware.   The notes here provide information about getting the damn video playback to work right in the Firefox web browser.   Note the version-specific characteristics. 

The screen below highlights a current issue.  Flash video is served when I edit this website, but when clients view the site, they are only shown HMTL5.   Up until recently, Flash video was used, and it works well and runs on all flavours of my equipment (Windows, Linux and Macbook).

Getting Firefox 60.2.1 to work properly - on Linux CentOS 6.6 (32-bit):

To do this, I had to upgrade from an older Firefox 34, to the bleeding edge Firefox 60.2.1 ESR (which means Extended Support Edition).  These are the only versions to bother with, as there is typically some stability with the ESR versions.  In 64-bit CentOS Linux, you can just use the Firefox 52.2 that is bundled with it.  You will probably have to install Adobe Flash support, for many webpages (eg: NHK English, the Ustream Live feed from the International Space Station, etc.)

To check:  HTML5 Video operation (Make sure you see all three "Big Buck Bunny" videos):

  https://www.quirksmode.org/html5/tests/video.html

To get HTML5 (and Adobe Flash) video to work, if you have older (but stable and fast) 32-bit machine, running CentOS 6.6, you probably want to upgrade to Firefox 60.2.1, via a "yum" or "dnf" (the new-and-improved? version of yum).   The key problem with doing this, is that Firefox 60.2.1 (the one that you get if you say "yum upgrade firefox" on CentOS 6.6), will probably crash if you try to import bookmarks.  And if you have your old bookmarks, they will *not* be transfered from your older Firefox to the new one.  (Why the folks writing Firefox cannot make bookmarks work right, looks to be due to their desire to force your bookmarking activity onto some alternate approach, like a cloud-service.  Perhaps the idea is to create a revenue stream?)  Whatever the reason, bookmarks are almost *always* broken on Firefox it seems.

Since even attempting to import an .html file of plain bookmarks in Firefox 60 will crash Firefox (see below), you will need to use some trickery to get your old bookmarks into the new Firefox 60.2.1. 

The reason for using Firefox 60 is that the video can be made to work, on Linux, which is useful.  Note: Again, you will likely need Adobe Flash, but it is not difficult to install on Linux.

Here are my notes on getting Firefox 60.2.1 to load your bookmarks.

-----------  MCL notes on bookmarks problem in FIrefox 60.2.1 ------------------------

Re; Bug # 1611808 "firefox 60 crashes when importing html files".  (on: https://bugzilla.redhat.com)

** Workaround **

Workaround to Firefox 60 crashing on importing .html bookmarks,
and failing to restore older bookmark backups (as .jsonlz4 files)

Firefox version: 60.2.1 ESR (Firefox Quantum)
Linux Verion (CentOS 6.6, 32-bit)
 (uname -a => 2.6.32-504.el6.i696 #1 SMP Wed. Oct. 15 03:02:07 UTC 2014 i686)
 
Summary:

I have figured out a workaround to this bug.  With a newly installed
Firefox 60.2.1, (resulting from a "yum update firefox"), I was unable
to import .html bookmarks, as this would cause Firefox to crash.

Attempts then, to restore from any of the "bookmarkbackups" files
from the previous Firefox (which was Firefox 34), resulted in no action.
No errors were produced, no messaged generated, and no restoration took
place.  

What did work, was using a web-available utility to convert the existing
bookmark-backup files (which are in ".jsonlz4" binary format), to HTML
files, and then importing the bookmarkbackups-generated .html file.


Details:

There is a utility which Jefferson Scher wrote, which can take a binary
".jsonlz4" file and convert it into HTML, and the resulting .html file,
*can* be successfully imported into Firefox 60.2.1.

URL of Bookmark Backup Reader/Decompressor for Firefox

  https://www.jeffersonscher.com/res/bookbackreader.html

I had roughly 1200 bookmarks, so this utility was a lifesaver.


How To Get previous-version Firefox Bookmarks into Firefox 60.2.1:
----------------------------------------------------------------------------------------------
Steps (for non-expert Linux users):  This assumes that "Import HTML
bookmarks" is crashing Firefox-60, and that "Restore Bookmarks" from
the ".jsonlz4" bookmarks in bookmarksbackup is also not working, as
is my situation:

 1) Locate your previous bookmarkbackups directory.  It will typically
    be under the local ".mozilla" directory, which on Linux will be a
    hidden directory, because of the "." character in front of the name.
    If your userid is "Smith", you can look in:

     /home/Smith/.mozilla/firefox/<random-string>.default/bookmarkbackups

    Note: In the "/home/Smith/.mozilla/firefox" you may have several of
    these "<random-string>.default" directories.  They are local-user
    directories for various versions of Firefox.  You can confirm which
    one is active, using "about:support" in your old Firefox version (before
    you attempt to update to Firefox 60).  The subdirectory "bookmarkbackups"
    appears to contain a backup of your bookmarks that looks like it is
    created when you use the "export bookmarks to .html file" option.

 2) Invoke the conversion site (from within old or new Firefox):

    https://www.jeffersonscher.com/res/bookbackreader.html

    It is called: "Bookmark Backup Reader/Decompressor for Firefox".
 
 3) Then list the binary ".jsonlz4" files in a desktop window using "Files"
    tool. Find program "Files" in "Applications" main option, sub-option:
    "Accessories". When "Files" starts, it will show your home directory.
    The .mozilla files will be hidden.  Click on the three-horizontal bars
    icon beside the "x" icon that closes the window. This will bring up an
    options menu that will have a blank check box "Show Hidden Files".  Check
    that box, and you will see ".mozilla" directory.  (The hidden ".yattayatta"
    directories will be at the end of the directory list).  Then, navigate
    to the  bookmarkbackup ".jsonlz4" file you want to convert, and click
    and drag it into the webpage box.  ( You should see a bunch of scrambled
    test fill the webpage window).

 4) Click the "Export HTML" button on the "Bookmark Backup Reader/Decompressor
    for Firefox" window.   The exported .html bookmark datafile will be
    called: "bookmarks_from_json.html".  In the subwindows that says:
    "Opening bookmarks_from_json.html", under the heading: "What should
    Firefox do with this file?", click the button that says: "Save file".
    You will then have to choose location.  Just use "Downloads" directory,
    which should be in your /home/<userid>/ directory.

 5) Now, in Firefox-60.2.1, you can successfully import *this* .html file,
    which was generated from the ".jsonlz4" binary.  I note on my machine,
    despite Firefox-60 indicating it would overwrite existing bookmarks, it
    in fact did not.  It appended the .html bookmarks to the existing ones,
    which is probably the correct thing to do.

The above procedure is the only way I was import .html bookmarks, or
restore the bookmarkbackups bookmarks into Firefox-60.2.1 ESR.

Hope this helps anyone else in a similar situation.
-------------------- MCL notes on Firefox 60.2.1 ESR on CentOS 6.6 Linux -------------------

Getting Firefox 47 working properly with Video - on Windows:

I run a version of Firefox that does not have .mp4 video rendering, and to make it work on my older WinXP/SP3 box, with both Flash and HTML5, I followed the instructions on this site, and they worked well.  As the test pages montage above show, I can render all common/popular video formats now.

http://www.msfn.org/board/topic/175591-enable-mp4-h264-aac-html5-video-in-firefox-on-windows-xp-without-flash/?_fromLogout=1

Hope this is useful.  I'm experimenting with verison 55.0.2 version of Firefox, but as the Mozilla folks have decided to drop support for all plugins, and are also taking a heavy-handed approach (again) at logging all one's web activity (the "Top Sites" stuff is back, and cannot be disabled in newer FF versions, apparently), I am remaining with this older version for now. 

Also, experiments on Android Firefox (which can have the Adobe Flash drivers successfully installed and made operational), show that Android 6.0.1 (current version for Samsung Tab-A) and Firefox 55.x version, are much less reliable than older Kitkat (Android version 4.4.2, running on Samsung Tab-3, with Firefox 40.x).  The Adobe Flash driver (version 11.1.115.81) can be installed on Android devices, as an .apk file, by following the instructions provided on the site below:

https://helpx.adobe.com/flash-player/kb/installing-flash-player-android-devices.html

I can confirm that Firefox version 55.0.2 (most current production Firefox, as of Sept. 14, 2017 from Google Play Store) with Android 6.0.1 on Samsung Tab-A (most current Andriod that Samsung official makes available for the device) works with the Android Flash drivers version 11.1.115.81, which are indicated on the Adobe documentation as only working on Android 4.0 (I don't know what sugar candy version this is ... Ice Cream Toad?).

The Flash Video archives from Adobe are at the url below.  You can find the Android Flash Ver 11.1.115.81 about 3/4 ers of the way down the page.  To download and install, make sure you fiddle the "Settings" in Android so that you can install .apk files (Android Package Files) from a non-certified source. 

https://helpx.adobe.com/flash-player/kb/archived-flash-player-versions.html

Hope this is useful.

Update: [ Oct. 25, 2017 ]  -  Thought I would put the image from the msfn site that has the details on how to get H.264 (mp4) stuff working here, since I see so much of the useful and honest info on the web going dark now.  In researching a related video issue, I was surprised at how much actively wrong information was being offered, especially on Youtube.  Since folks are getting paid for generating video-views, the whole youtube ecosystem is becoming about as accurate and useful as the "sideshow" booths at the CNE that I saw as a child.  These were almost 19th-century displays of fake crap that cost a quarter, or were simple rigged games that offered low-quality payoffs even for a win.  Real carney stuff.  Youtube videos that purport to offer explanations or fixes, are often little more than sideshow-style disinfo to attract the eyeballs of the lazy.  Sad.  The internet was this great idea, that is turning into a smelly garbage-dump of fraud and disinfo before our very eyes. <Sigh..>.   I found and used this info below to get Firefox47+HTML5 H264 video stuff working right on an older Windows box, and thought I should offer the page image, in the event the msfn site goes dark - as this site here may well do soon.  Copy it, and get the Adobe stuff while you can.  I am migrating all our material over to Linux platforms (CentOS 6 and 7 series is probably best choice), but we still have a mixed bag of machines.  (A new ACER running Windows-10 is so amazingly awful and annoying, that it is comical - but that is another story for another time.)...

Detailed image-capture of info to configure Firefox to render H.264 (mp4) videos (eg. modern Youtube, as of Oct. 2017), correctly.  Test your Youtube rendering with the page "https://www.youtube.com/html5".  Once you get Firefox and the Primetime plugin from Adobe working right, you should see checkmarks in all 6 boxers on the Youtube HTML5 test screen.

Overview of What I had to do:

1) FIrst, get the plugin zip file.  I got a copy at this (backup) location, via the "wayback" machine.  The URL is:

https://web.archive.org/web/20170718145441/http://sdfox7.com/xp/sp3/EOL/primetime_gmp_win_x86_gmc_40673.zip

2) Put the zip file somewhere, and run a SHA256 check against it to confirm the hash-code that is provided on the video image.  It should start with 80975242 and end with BAB11395.  Unzip the downloaded file "primetime_gmp_win_x86_gmc_40673" and you should get three files, which are called:  eme-adobe.dll, eme-adobe.info, and eme-adobe.voucher.  These three files will have to be put into the right subdirectory in your Firefox Profile directory.

3) Install the plugin manually:  Start your Firefox, and look for where your "Profile" directory is located.  Enter "about:support" in the url box, and then, in the section called "Application Basics" click on the button beside "Profile Folder" that says: "Show Profile".  That is your profile directory.

4) In your Firefox profile directory, where the plugins are located, create a directory called "gmp-eme-adobe".  Go into that directory, and create a sub-directory called "17",and then navigate into that "17" directory you just created. 

5) Put the three files from the zip file into this new "17" subdirectory.  That's it.  You can exit the directory stuff, and in the Firefox URL box, enter: "about:config", to change the Firefox operational control parameters.  Click thru the "I'll be careful..." warning.  Make sure to be careful, eh?

6) Enter "media" in the search box, to display all the "media.<blahblahblah...>" parameters.  You will have to examine the "media.gmp...." parms shown in the screen below, and make sure your Firefox parms match these shown on that screen.  You need to BE ACCURATE.  Some parms are booleans, some are integers and some are strings.  In all cases, these terms are CASE SENSITIVE.  That means "media.gmp-yattayatta" is NOT THE SAME AS "media.gmp-yattaYatta".  Why these fine fellows mix case randomly is beyond me, but just deal with it.

7) Once you get this done (did I stress the CASE SENSITIVE thing?), you should be able to shut down Firefox, restart it, and the plugin should be installed and it should work.  You can check status of installed plugins with: "about:plugins", or just select "Tools / Add-ons / Plugins" from the top-line drop down Firefox menu.   Check status by displaying: "https://www.youtube.com/html5" and you can also check the 1-minute test videos of "Big Bucks Bunny" at "http://www.quirksmode.org/html5/tests/video.html".  (The results of the tests for my config are shown in first screen image at beginning of this section.)

Again, hope this helps.  I have spent *way* too much time on this video stuff, even building Mplayer and GMplayer from source, for my Linux boxes - and yes, got it working very nicely, in hi-res video and audio.  (I'll doc what I did in detail to get it working right at some point.)  I run the audio thru an old Denon amp that has a transformer the size of a small car-battery, and push it out thru 35 year old Ortofon 445 speakers that apparently were made in Denmark.  It all finally looks and sounds somewhat OK.  Problem is that any interesting video has to be downloaded, as youtube stops and starts with interuptions far too often.  It is sometimes unwatchable, but at least we are not using satellite, which other folks tell me is even worse in bad weather, than our poor Wimax service.