diff -up firefox-75.0/extensions/pref/autoconfig/src/nsReadConfig.cpp.1170092 firefox-75.0/extensions/pref/autoconfig/src/nsReadConfig.cpp

--- firefox-75.0/extensions/pref/autoconfig/src/nsReadConfig.cpp.1170092	2020-04-03 21:34:41.000000000 +0200

+++ firefox-75.0/extensions/pref/autoconfig/src/nsReadConfig.cpp	2020-04-06 22:40:02.760674871 +0200

@@ -244,8 +244,20 @@ nsresult nsReadConfig::openAndEvaluateJS

     if (NS_FAILED(rv)) return rv;

     rv = NS_NewLocalFileInputStream(getter_AddRefs(inStr), jsFile);

-    if (NS_FAILED(rv)) return rv;

+    if (NS_FAILED(rv)) {

+      // Look for cfg file in /etc/<application>/pref

+      rv = NS_GetSpecialDirectory(NS_APP_PREFS_SYSTEM_CONFIG_DIR,

+                                  getter_AddRefs(jsFile));

+      NS_ENSURE_SUCCESS(rv, rv);

+

+      rv = jsFile->AppendNative(nsLiteralCString("pref"));

+      NS_ENSURE_SUCCESS(rv, rv);

+      rv = jsFile->AppendNative(nsDependentCString(aFileName));

+      NS_ENSURE_SUCCESS(rv, rv);

+      rv = NS_NewLocalFileInputStream(getter_AddRefs(inStr), jsFile);

+      NS_ENSURE_SUCCESS(rv, rv);

+    }

   } else {

     nsAutoCString location("resource://gre/defaults/autoconfig/");

     location += aFileName;

diff -up firefox-75.0/modules/libpref/Preferences.cpp.1170092 firefox-75.0/modules/libpref/Preferences.cpp

--- firefox-75.0/modules/libpref/Preferences.cpp.1170092	2020-04-06 22:40:02.761674865 +0200

+++ firefox-75.0/modules/libpref/Preferences.cpp	2020-04-06 22:40:57.675325227 +0200

@@ -4468,6 +4468,9 @@ nsresult Preferences::InitInitialObjects

   //

   // Thus, in the omni.jar case, we always load app-specific default

   // preferences from omni.jar, whether or not `$app == $gre`.

+  //

+  // At very end load configuration from system config location:

+  // - /etc/firefox/pref/*.js

   nsresult rv = NS_ERROR_FAILURE;

   UniquePtr<nsZipFind> find;

diff -up firefox-75.0/toolkit/xre/nsXREDirProvider.cpp.1170092 firefox-75.0/toolkit/xre/nsXREDirProvider.cpp

--- firefox-75.0/toolkit/xre/nsXREDirProvider.cpp.1170092	2020-04-03 21:35:39.000000000 +0200

+++ firefox-75.0/toolkit/xre/nsXREDirProvider.cpp	2020-04-06 22:40:02.761674865 +0200

@@ -60,6 +60,7 @@

 #endif

 #ifdef XP_UNIX

 #  include <ctype.h>

+#  include "nsIXULAppInfo.h"

 #endif

 #ifdef XP_IOS

 #  include "UIKitDirProvider.h"

@@ -533,6 +534,21 @@ nsXREDirProvider::GetFile(const char* aP

       }

     }

   }

+

+#if defined(XP_UNIX)

+  if (!strcmp(aProperty, NS_APP_PREFS_SYSTEM_CONFIG_DIR)) {

+    nsCString sysConfigDir = nsLiteralCString("/etc/");

+    nsCOMPtr<nsIXULAppInfo> appInfo = do_GetService("@mozilla.org/xre/app-info;1");

+    if (!appInfo)

+      return NS_ERROR_NOT_AVAILABLE;

+    nsCString appName;

+    appInfo->GetName(appName);

+    ToLowerCase(appName);

+    sysConfigDir.Append(appName);

+    return NS_NewNativeLocalFile(sysConfigDir, false, aFile);

+  }

+#endif

+

   if (NS_FAILED(rv) || !file) return NS_ERROR_FAILURE;

   if (ensureFilePermissions) {

@@ -845,6 +861,16 @@ nsresult nsXREDirProvider::GetFilesInter

     LoadDirIntoArray(mXULAppDir, kAppendPrefDir, directories);

+    // Add /etc/<application>/pref/ directory if it exists

+    nsCOMPtr<nsIFile> systemPrefDir;

+    rv = NS_GetSpecialDirectory(NS_APP_PREFS_SYSTEM_CONFIG_DIR,

+                                getter_AddRefs(systemPrefDir));

+    if (NS_SUCCEEDED(rv)) {

+      rv = systemPrefDir->AppendNative(nsLiteralCString("pref"));

+      if (NS_SUCCEEDED(rv))

+        directories.AppendObject(systemPrefDir);

+    }

+

     rv = NS_NewArrayEnumerator(aResult, directories, NS_GET_IID(nsIFile));

   } else if (!strcmp(aProperty, NS_APP_CHROME_DIR_LIST)) {

     // NS_APP_CHROME_DIR_LIST is only used to get default (native) icons

diff -up firefox-75.0/xpcom/io/nsAppDirectoryServiceDefs.h.1170092 firefox-75.0/xpcom/io/nsAppDirectoryServiceDefs.h

--- firefox-75.0/xpcom/io/nsAppDirectoryServiceDefs.h.1170092	2020-04-03 21:35:39.000000000 +0200

+++ firefox-75.0/xpcom/io/nsAppDirectoryServiceDefs.h	2020-04-06 22:40:02.761674865 +0200

@@ -60,6 +60,7 @@

 #define NS_APP_PREFS_DEFAULTS_DIR_LIST "PrefDL"

 #define NS_APP_PREFS_OVERRIDE_DIR \

   "PrefDOverride"  // Directory for per-profile defaults

+#define NS_APP_PREFS_SYSTEM_CONFIG_DIR          "PrefSysConf"   // Directory with system-wide configuration

 #define NS_APP_USER_PROFILE_50_DIR "ProfD"

 #define NS_APP_USER_PROFILE_LOCAL_50_DIR "ProfLD"