[Firefox] Generate a default-prefs file that can be used directly in mozilla-central (bug 1780609)

[Snuffleupagus]

No description provided.

[Snuffleupagus]

Please note: This will obviously require changes in the mozilla-central code as well, so needs to land simultaneously in GitHub/Bugzilla, however I'll probably need some guidance w.r.t. how the mozilla-central part should look to integrate correctly with the prefs-system.

The file that's generated looks like this:

/* Copyright 2022 Mozilla Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

//
// THIS FILE IS GENERATED AUTOMATICALLY, DO NOT EDIT MANUALLY!
//

pref("pdfjs.annotationEditorMode", -1);
pref("pdfjs.annotationMode", 2);
pref("pdfjs.cursorToolOnLoad", 0);
pref("pdfjs.defaultZoomValue", "");
pref("pdfjs.disablePageLabels", false);
pref("pdfjs.enablePermissions", false);
pref("pdfjs.enablePrintAutoRotate", true);
pref("pdfjs.enableScripting", true);
pref("pdfjs.externalLinkTarget", 0);
pref("pdfjs.historyUpdateUrl", false);
pref("pdfjs.ignoreDestinationZoom", false);
pref("pdfjs.forcePageColors", false);
pref("pdfjs.pageColorsBackground", "Canvas");
pref("pdfjs.pageColorsForeground", "CanvasText");
pref("pdfjs.pdfBugEnabled", false);
pref("pdfjs.sidebarViewOnLoad", -1);
pref("pdfjs.scrollModeOnLoad", -1);
pref("pdfjs.spreadModeOnLoad", -1);
pref("pdfjs.textLayerMode", 1);
pref("pdfjs.useOnlyCssZoom", false);
pref("pdfjs.viewerCssTheme", 0);
pref("pdfjs.viewOnLoad", 0);
pref("pdfjs.disableAutoFetch", false);
pref("pdfjs.disableFontFace", false);
pref("pdfjs.disableRange", false);
pref("pdfjs.disableStream", false);
pref("pdfjs.enableXfa", true);