What's in my Firefox config to cause youtube not pre-buffer?

Question

I made a 'user-config' file for my Firefox to improve security and performance, but I find YouTube only continues buffering when it reaches the end of the current buffered content, this causes significant interruptions through the entire video, could anyone tell me which is wrong?

This is the beginning of the pref.js:

# Mozilla User Preferences

/* Do not edit this file.
 *
 * If you make changes to this file while the application is running,
 * the changes will be overwritten when the application exits.
 *
 * To make a manual change to preferences, you can visit the URL about:config
 */

user_pref("accessibility.accesskeycausesactivation", false);
user_pref("accessibility.typeaheadfind.flashBar", 0);
user_pref("app.update.auto", false);
user_pref("beacon.enabled", false);
user_pref("browser.backspace_action", 1);
user_pref("browser.bookmarks.restore_default_bookmarks", false);
user_pref("browser.cache.disk.smart_size.first_run", false);
user_pref("browser.cache.disk.smart_size.use_old_max", false);
user_pref("browser.cache.offline.enable", false);
user_pref("browser.customizemode.tip0.shown", true);
user_pref("browser.download.importedFromSqlite", true);
user_pref("browser.download.manager.addToRecentDocs", false);
user_pref("browser.download.panel.shown", true);
user_pref("browser.download.useDownloadDir", false);
user_pref("browser.formfill.enable", false);
user_pref("browser.link.open_newwindow.restriction", 0);
user_pref("browser.migrated-sync-button", true);
user_pref("browser.migration.version", 40);
user_pref("browser.newtabpage.enhanced", false);
user_pref("browser.newtabpage.storageVersion", 1);
user_pref("browser.pagethumbnails.capturing_disabled", true);
user_pref("browser.places.smartBookmarksVersion", 8);
user_pref("browser.reader.detectedFirstArticle", true);
user_pref("browser.rights.3.shown", true);
user_pref("browser.search.countryCode", "US");
user_pref("browser.search.defaultenginename.US", "data:text/plain,browser.search.defaultenginename.US=Google");
user_pref("browser.search.geoSpecificDefaults", false);
user_pref("browser.search.region", "US");
user_pref("browser.search.suggest.enabled", false);
user_pref("browser.send_pings.require_same_host", true);
user_pref("browser.sessionstore.privacy_level", 2);
user_pref("browser.shell.checkDefaultBrowser", false);
user_pref("browser.startup.homepage_override.mstone", "50.0.1");
user_pref("browser.toolbarbuttons.introduced.pocket-button", true);
user_pref("browser.translation.engine", "google");
user_pref("browser.uiCustomization.state", "{\"placements\":{\"PanelUI-contents\":[\"search-container\",\"edit-controls\",\"zoom-controls\",\"new-window-button\",\"privatebrowsing-button\",\"save-page-button\",\"print-button\",\"history-panelmenu\",\"fullscreen-button\",\"find-button\",\"preferences-button\",\"add-ons-button\",\"developer-button\",\"sync-button\"],\"addon-bar\":[\"addonbar-closebutton\",\"status-bar\"],\"PersonalToolbar\":[\"personal-bookmarks\"],\"nav-bar\":[\"urlbar-container\",\"bookmarks-menu-button\",\"downloads-button\",\"home-button\"],\"TabsToolbar\":[\"tabbrowser-tabs\",\"new-tab-button\",\"alltabs-button\"],\"toolbar-menubar\":[\"menubar-items\"]},\"seen\":[\"developer-button\"],\"dirtyAreaCache\":[\"PersonalToolbar\",\"nav-bar\",\"TabsToolbar\",\"toolbar-menubar\",\"PanelUI-contents\",\"addon-bar\"],\"currentVersion\":6,\"newElementCount\":0}");
user_pref("camera.control.face_detection.enabled", false);
user_pref("datareporting.healthreport.uploadEnabled", false);
user_pref("datareporting.policy.dataSubmissionEnabled", false);
user_pref("device.sensors.enabled", false);
user_pref("devtools.remote.wifi.scan", false);
user_pref("devtools.remote.wifi.visible", false);
user_pref("dom.apps.reset-permissions", true);
user_pref("dom.battery.enabled", false);
user_pref("dom.caches.enabled", false);
user_pref("dom.disable_window_open_feature.menubar", true);
user_pref("dom.disable_window_open_feature.personalbar", true);
user_pref("dom.disable_window_open_feature.titlebar", true);
user_pref("dom.disable_window_open_feature.toolbar", true);
user_pref("dom.enable_performance", false);
user_pref("dom.enable_resource_timing", false);
user_pref("dom.enable_user_timing", false);
user_pref("dom.event.clipboardevents.enabled", false);
user_pref("dom.gamepad.enabled", false);
user_pref("dom.idle-observers-api.enabled", false);
user_pref("dom.push.connection.enabled", false);
user_pref("dom.push.enabled", false);
user_pref("dom.vr.oculus.enabled", false);
user_pref("dom.vr.oculus050.enabled", false);
user_pref("experiments.activeExperiment", false);
user_pref("experiments.enabled", false);
user_pref("experiments.supported", false);
user_pref("extensions.pocket.enabled", false);
user_pref("extensions.shownSelectionUI", true);
user_pref("geo.enabled", false);
user_pref("media.getusermedia.browser.enabled", false);
user_pref("media.getusermedia.screensharing.enabled", false);
user_pref("media.hardware-video-decoding.failed", false);
user_pref("media.navigator.enabled", false);
user_pref("media.peerconnection.enabled", false);
user_pref("narrate.enabled", false);
user_pref("network.allow-experiments", false);
user_pref("network.cookie.cookieBehavior", 3);
user_pref("network.cookie.prefsMigrated", true);
user_pref("network.cookie.thirdparty.sessionOnly", true);
user_pref("network.disable.ipc.security", false);
user_pref("network.http.max-connections", 1500);
user_pref("network.http.max-connections-per-server", 96);
user_pref("network.http.max-persistent-connections-per-proxy", 128);
user_pref("network.http.max-persistent-connections-per-server", 64);
user_pref("network.http.pipelining", true);
user_pref("network.http.pipelining.maxrequests", 64);
user_pref("network.http.pipelining.ssl", true);
user_pref("network.http.proxy.pipelining", true);
user_pref("network.http.referer.XOriginPolicy", 1);
user_pref("network.http.referer.spoofSource", true);
user_pref("network.http.referer.trimmingPolicy", 1);
user_pref("network.http.sendRefererHeader", 1);
user_pref("network.http.spdy.default-concurrent", 400);
user_pref("network.http.spdy.enabled.v3-1", true);
user_pref("network.predictor.cleaned-up", true);
user_pref("network.predictor.enabled", false);
user_pref("network.proxy.socks_remote_dns", true);
user_pref("network.websocket.max-connections", 400);
user_pref("offline-apps.allow_by_default", false);
user_pref("pdfjs.previousHandler.alwaysAskBeforeHandling", true);
user_pref("pref.privacy.disable_button.change_blocklist", false);
user_pref("pref.privacy.disable_button.view_passwords", false);
user_pref("pref.privacy.disable_button.view_passwords_exceptions", false);
user_pref("privacy.clearOnShutdown.offlineApps", true);
user_pref("privacy.clearOnShutdown.openWindows", true);
user_pref("privacy.clearOnShutdown.siteSettings", true);
user_pref("privacy.cpd.offlineApps", true);
user_pref("privacy.cpd.passwords", true);
user_pref("privacy.cpd.siteSettings", true);
user_pref("privacy.donottrackheader.enabled", true);
user_pref("privacy.sanitize.timeSpan", 0);
user_pref("privacy.trackingprotection.enabled", true);
user_pref("privacy.trackingprotection.introCount", 20);
user_pref("privacy.trackingprotection.ui.enabled", true);
user_pref("security.disable_button.openCertManager", false);
user_pref("security.ssl.treat_unsafe_negotiation_as_broken", true);
user_pref("services.sync.migrated", true);
user_pref("signon.rememberSignons", false);
user_pref("social.remote-install.enabled", false);
user_pref("social.share.activationPanelEnabled", false);
user_pref("toolkit.telemetry.archive.enabled", false);
user_pref("toolkit.telemetry.reportingpolicy.firstRun", false);
user_pref("toolkit.telemetry.unified", false);
user_pref("webgl.disable-extensions", true);

Answer 1

What you need is a script to disable dash playback. Use the YouTube centre addon

Then on the YouTube home page you should see a gear icon. Click on that and then under external players untick Dash playback. Dash playback setting

What Dash playback does is that it buffers the video as its playing. This can cause a lot of buffering issues.

Answer 2

In address bar, type about:config ~ Click Accept. In search bar, type mp4 - you will find media.mediasource.mp4.enabled, Set it to false.

This will fix the YouTube video problems. Some sites that play videos will need it enabled, so it will need set to true again to make those videos work. It is an Adobe Flash, HTML5 thing. So make a text folder and set it on your desktop with the info I gave you so if you need this info in the future you will have it. Remember this, about:config is the heart of the Firefox browser, so unless you know what you're doing, don't go changing values in there, or it can make Firefox an unhappy camper. LOL! Hope this helps You, and all! Regards!