Hello dencorso
Please accept my apologies I wrote from memory, thus I failed miserably...
Plus, my XP (SP2) box has been decommissioned since last November, so was not
practical for me to test there, only tested on Vista SP2 without the PUS.
So Fx 45.0.1 is definitely not working! But here are the full details:
I used to frequent the mozillazine forums and it was there I became aware of the
following bugzilla bug #1234099 ;
it was this bug (and its title: Unhide Adobe GMP on Windows XP)
I had in my mind when I posted here with regards to your issue...
Sadly, I had not checked that bug's recent activity; it was "uplifted" to version 46,
which brings us in turn to Bugzilla bug #1250766 ; comment 6 writes:
... and comment 12 writes:
Today is/was a Sunday, so had some more spare time at hand; I decided to bring my XP SP2 x86 box
out of storage and try myself - I installed first Firefox 46.0b9 portable and then Firefox Developer Edition
(DevEd for brevity) 47.0a2[20160410] portable (both in PAF format, with separate profiles).
In both Firefox versions, there is a "Primetime CDM provided by Adobe Systems Incorporated 17" entry in
about:addons -> plugins, also in the profile folder exists a "gmp-eme-adobe" directory with "eme-adobe.dll".
about:config has "media.gmp-eme-adobe.enabled;true". But about:preferences#content does not show a
"Playback DRM content" section!
I tried to play back some local MP4 files, first in Fx 46.0b9 and then in DevEd 47.0a2.
In both cases, playback failed, in contrast to what is stated inside #1250766.
In the case of DevEd 47.0a2, browser suffers a silent crash: Firefox 47.0a2 Crash Report [@ mozilla::gmp::GMPChild::ProcessingError ]
everytime I try a new MP4/M4A file.
Perhaps my failure stems from the fact I'm still on SP2 (32bit), but I did not care to debug this further...
You don't stand to lose anything if you yourself try versions DevEd 47.0a2_x86 or even Nightly 48.0a1_x86
(you can use the portables without affecting your normal Fx install) - perhaps in your case, with SP3(/4)
installed, you may have better results. Comment 12 only mentions a test on XP (SP2) x64, so 32bit XP is
not explicitly covered in that comment...
Since you are very keen on having this working (playback of h264/aac in MP4 in Firefox on XP),
perhaps you should join referenced Bugzilla bug and share your findings there...
It appears the Mozilla Devs want this as much as you...
Anyhow, again sorry for the initial false info, I do hope you soon get this sorted !
Many regards