Problems with youtube in firefox with windows 8 and 8.1

Question

Lately i sell some computers with windows 8, and windows 8.1, so they are fresh install. and i have problems with the videos under youtube, but just with firefox, with chrome works ok, with internet explorer the same, no problem. The problem when i'm using the pluging of flash, is the next:
start the reproduction of the video with the default resolution in my case of 360, but after of a few seconds, 6 or 7, the reproduction jump to the lower resolution available (240 by example), and after other few seconds, do the same jump to a lower resolution, few seconds againd and jump to higher resolutions available, maybe 480, and so until try with every resolution available in the video and after of that show the next message:
"Se ha producido un error, vuelve a intentarlo mas tarde"
The messaage is in spanish because i'm using spanish versions to sell, well, just say that a error arised and try later.
well i think maybe problems with the pluging of flash, i will try with the html5 support, then i enable the html5 support in youtube.
And still with problems but a little different the video start with the default resolution (360), and after a few seconds maybe 3 or 4, the video stop, maybe 1 second and later continue by other 2 or 3 seconds of video and stop again other second, and continue on this way until the end of the video.
I dont have problems with the network, i can see the videows without problems with other computers in the same network, or with mobile devices, but the problem is just with firefox.
Isnt virus, because the installation is clean, i dont have extra software because the first times i think that would be by a extra software, then just clean installation of windows 8 and 8.1 and firefox, the problem i try versions since the 29 until now that the latest is the 33, the same problem, exactly in the same way, and doesn't help of nothing update the drivers of the motherboard or even install every update of windows.
Procesador Intel(R) Pentium(R) CPU G2030 @ 3.00GHz
motherboard gigabyte GA-H61M-DS2
MEMORY 4gb RAM DDR·3
Hard disk 500GB Seagate.
with this same configuration i dont have problem if i have installed windows 7.
I guess isnt a problem of hardware, because the other browsers can display the videos without any problem.
- the latest version of mozilla firefox in every time.
- I try every thing, clear cache, disable acceleration, update drivers, update windows, uninstall and reinstall, even format the machine again.
I see other posts of people with similar problems, but without 1 good answer, just a lot of general solutions that doesnt work.
i must confese that i dont test yet with other hardware and same software.
I hope someone can help me.
No big problem for me, because i dont use these computers, but i like use firefox, and if i had that problem in my computer i would be crazy trying to find a fix to the problem.

Answer 1

The data of my firefox is this one, dont know if this can be of utility, in this moment i install the addblock, but the problem was since the installation was clean. then this doesnt affect in the result.
Thank's
"application": {
"name": "Firefox",
"version": "33.0",
"userAgent": "Mozilla/5.0 (Windows NT 6.3; WOW64; rv:33.0) Gecko/20100101 Firefox/33.0",
"supportURL": "https://support.mozilla.org/1/firefox/33.0/WINNT/es-MX/",
"numTotalWindows": 1,
"numRemoteWindows": 0
"crashes": {
"submitted": [],
"pending": 0
"modifiedPreferences": {
"browser.cache.disk.capacity": 358400,
"browser.cache.disk.smart_size.first_run": false,
"browser.cache.frecency_experiment": 3,
"browser.places.smartBookmarksVersion": 7,
"browser.sessionstore.upgradeBackup.latestBuildID": "20141011015303",
"browser.startup.homepage_override.mstone": "33.0",
"browser.startup.homepage": "about:home",
"browser.startup.homepage_override.buildID": "20141011015303",
"extensions.lastAppVersion": "33.0",
"gfx.direct3d.last_used_feature_level_idx": 0,
"media.gmp-gmpopenh264.lastUpdate": 1413506428,
"media.gmp-gmpopenh264.version": "1.1",
"media.gmp-manager.lastCheck": 1413975157,
"network.cookie.prefsMigrated": true,
"places.history.expiration.transient_current_max_pages": 99545,
"plugin.disable_full_page_plugin_for_types": "application/pdf",
"plugin.importedState": true,
"privacy.sanitize.timeSpan": 0,
"privacy.sanitize.migrateFx3Prefs": true
"lockedPreferences": {},
"graphics": {
"numTotalWindows": 1,
"numAcceleratedWindows": 1,
"windowLayerManagerType": "Direct3D 11",
"windowLayerManagerRemote": true,
"adapterDescription": "Intel(R) HD Graphics",
"adapterVendorID": "0x8086",
"adapterDeviceID": "0x0152",
"adapterRAM": "Unknown",
"adapterDrivers": "igdumdim64 igd10iumd64 igd10iumd64 igdumdim32 igd10iumd32 igd10iumd32",
"driverVersion": "10.18.10.3621",
"driverDate": "5-16-2014",
"adapterDescription2": "",
"adapterVendorID2": "",
"adapterDeviceID2": "",
"adapterRAM2": "",
"adapterDrivers2": "",
"driverVersion2": "",
"driverDate2": "",
"isGPU2Active": false,
"direct2DEnabled": true,
"directWriteEnabled": true,
"directWriteVersion": "6.3.9600.17111",
"webglRenderer": "Google Inc. -- ANGLE (Intel(R) HD Graphics Direct3D9Ex vs_3_0 ps_3_0)",
"info": {
"AzureCanvasBackend": "direct2d",
"AzureSkiaAccelerated": 0,
"AzureFallbackCanvasBackend": "cairo",
"AzureContentBackend": "direct2d"
"javaScript": {
"incrementalGCEnabled": true
"accessibility": {
"isActive": false,
"forceDisabled": 0
"libraryVersions": {
"NSPR": {
"minVersion": "4.10.7",
"version": "4.10.7"
"NSS": {
"minVersion": "3.17.1 Basic ECC",
"version": "3.17.1 Basic ECC"
"NSSUTIL": {
"minVersion": "3.17.1",
"version": "3.17.1"
"NSSSSL": {
"minVersion": "3.17.1 Basic ECC",
"version": "3.17.1 Basic ECC"
"NSSSMIME": {
"minVersion": "3.17.1 Basic ECC",
"version": "3.17.1 Basic ECC"
"userJS": {
"exists": false
"extensions": [
"name": "Adblock Edge",
"version": "2.1.5",
"isActive": true,
"id": "{fe272bd1-5f76-4ea4-8501-a05d35d823fc}"
"experiments": []
}