diff --git a/extensions/pref/autoconfig/moz.build b/extensions/pref/autoconfig/moz.build
index 0ef8aad2a969..a8292ea733d9 100644
--- a/extensions/pref/autoconfig/moz.build
+++ b/extensions/pref/autoconfig/moz.build
@@ -6,6 +6,6 @@
 
 DIRS += ["src"]
 
-XPCSHELL_TESTS_MANIFESTS += ["test/unit/xpcshell.ini"]
+XPCSHELL_TESTS_MANIFESTS += ["test/unit/xpcshell.ini", "test/unit/xpcshell_snap.ini"]
 
 MARIONETTE_UNIT_MANIFESTS += ["test/marionette/manifest.ini"]
diff --git a/extensions/pref/autoconfig/src/nsReadConfig.cpp b/extensions/pref/autoconfig/src/nsReadConfig.cpp
index 39d1930add7d..06f54dd0ab77 100644
--- a/extensions/pref/autoconfig/src/nsReadConfig.cpp
+++ b/extensions/pref/autoconfig/src/nsReadConfig.cpp
@@ -26,6 +26,10 @@
 #include "nspr.h"
 #include "nsXULAppAPI.h"
 
+#if defined(MOZ_WIDGET_GTK)
+#  include "mozilla/WidgetUtilsGtk.h"
+#endif  // defined(MOZ_WIDGET_GTK)
+
 using namespace mozilla;
 
 extern bool sandboxEnabled;
@@ -243,7 +247,16 @@ nsresult nsReadConfig::openAndEvaluateJSFile(const char* aFileName,
   nsCOMPtr<nsIInputStream> inStr;
   if (isBinDir) {
     nsCOMPtr<nsIFile> jsFile;
-    rv = NS_GetSpecialDirectory(NS_GRE_DIR, getter_AddRefs(jsFile));
+#if defined(MOZ_WIDGET_GTK)
+    if (!mozilla::widget::IsRunningUnderFlatpakOrSnap()) {
+#endif  // defined(MOZ_WIDGET_GTK)
+      rv = NS_GetSpecialDirectory(NS_GRE_DIR, getter_AddRefs(jsFile));
+#if defined(MOZ_WIDGET_GTK)
+    } else {
+      rv = NS_GetSpecialDirectory(NS_OS_SYSTEM_CONFIG_DIR,
+                                  getter_AddRefs(jsFile));
+    }
+#endif  // defined(MOZ_WIDGET_GTK)
     if (NS_FAILED(rv)) return rv;
 
     rv = jsFile->AppendNative(nsDependentCString(aFileName));
diff --git a/extensions/pref/autoconfig/test/unit/autoconfig-snap.cfg b/extensions/pref/autoconfig/test/unit/autoconfig-snap.cfg
new file mode 100644
index 000000000000..c5c67bfbb7bb
--- /dev/null
+++ b/extensions/pref/autoconfig/test/unit/autoconfig-snap.cfg
@@ -0,0 +1,4 @@
+// # don't remove this comment! (the first line is ignored by Mozilla)
+
+// Verify this one has a user value
+pref("_autoconfig_.test.userpref-snap", "userpref-snap");
diff --git a/extensions/pref/autoconfig/test/unit/autoconfig_snap.js b/extensions/pref/autoconfig/test/unit/autoconfig_snap.js
new file mode 100644
index 000000000000..bfa1df485955
--- /dev/null
+++ b/extensions/pref/autoconfig/test/unit/autoconfig_snap.js
@@ -0,0 +1,5 @@
+/* global pref */
+pref("general.config.sandbox_enabled", true);
+pref("general.config.filename", "autoconfig-snap.cfg");
+pref("general.config.vendor", "autoconfig-snap");
+pref("general.config.obscure_value", 0);
diff --git a/extensions/pref/autoconfig/test/unit/test_autoconfig_custom_path.js b/extensions/pref/autoconfig/test/unit/test_autoconfig_custom_path.js
new file mode 100644
index 000000000000..bad16e39dba2
--- /dev/null
+++ b/extensions/pref/autoconfig/test/unit/test_autoconfig_custom_path.js
@@ -0,0 +1,23 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const { updateAppInfo } = ChromeUtils.import(
+  "resource://testing-common/AppInfo.jsm"
+);
+
+function run_test() {
+  let env = Cc["@mozilla.org/process/environment;1"].getService(
+    Ci.nsIEnvironment
+  );
+
+  let testDirName = do_get_cwd().clone();
+  env.set("MOZ_SYSTEM_CONFIG_DIR", testDirName.path);
+
+  updateAppInfo();
+
+  let customSysConfD = Services.dirsvc.get("SysConfD", Ci.nsIFile);
+  let parent = customSysConfD.parent;
+  let child = customSysConfD.leafName;
+  notEqual("/etc", parent.path, "SysConfD is not in /etc");
+  equal("xpcshell", child, "SysConfD is xpcshell");
+}
diff --git a/extensions/pref/autoconfig/test/unit/test_autoconfig_default_path.js b/extensions/pref/autoconfig/test/unit/test_autoconfig_default_path.js
new file mode 100644
index 000000000000..54cf58847a78
--- /dev/null
+++ b/extensions/pref/autoconfig/test/unit/test_autoconfig_default_path.js
@@ -0,0 +1,13 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const { updateAppInfo } = ChromeUtils.import(
+  "resource://testing-common/AppInfo.jsm"
+);
+
+function run_test() {
+  updateAppInfo();
+
+  let defaultSysConfD = Services.dirsvc.get("SysConfD", Ci.nsIFile);
+  equal("/etc/xpcshell", defaultSysConfD.path, "SysConfD is in /etc");
+}
diff --git a/extensions/pref/autoconfig/test/unit/test_autoconfig_snap.js b/extensions/pref/autoconfig/test/unit/test_autoconfig_snap.js
new file mode 100644
index 000000000000..cd6003cf93e2
--- /dev/null
+++ b/extensions/pref/autoconfig/test/unit/test_autoconfig_snap.js
@@ -0,0 +1,80 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/* eslint no-unsafe-finally: "off"*/
+/* Turning off this rule to allow control flow operations in finally block
+ * http://eslint.org/docs/rules/no-unsafe-finally  */
+
+const { updateAppInfo } = ChromeUtils.import(
+  "resource://testing-common/AppInfo.jsm"
+);
+
+function ensureRemove(file) {
+  try {
+    file.remove(false);
+  } catch (e) {
+    if (e.result != Cr.NS_ERROR_FILE_NOT_FOUND) {
+      throw e;
+    }
+  }
+}
+
+async function run_test() {
+  let env = Cc["@mozilla.org/process/environment;1"].getService(
+    Ci.nsIEnvironment
+  );
+  let prefs = Services.prefs.getBranch(null);
+
+  let testDir = do_get_cwd();
+  let confDir = testDir.clone();
+  confDir.append("MozSystemConfigDir");
+  env.set("MOZ_SYSTEM_CONFIG_DIR", confDir.path);
+  env.set("SNAP_INSTANCE_NAME", "xpcshell");
+
+  updateAppInfo();
+
+  let sysConfD = Services.dirsvc.get("SysConfD", Ci.nsIFile);
+
+  let defaultPrefDExtra = sysConfD.clone();
+  defaultPrefDExtra.append("defaults");
+  defaultPrefDExtra.append("pref");
+
+  await IOUtils.makeDirectory(defaultPrefDExtra.path);
+
+  const kAutoConfigFile = defaultPrefDExtra.clone();
+  kAutoConfigFile.append("autoconfig_snap.js");
+  const kAutoConfigCfg = sysConfD.clone();
+  kAutoConfigCfg.append("autoconfig-snap.cfg");
+
+  let autoConfigJS = testDir.clone();
+  autoConfigJS.append(kAutoConfigFile.leafName);
+
+  let autoConfigCfg = testDir.clone();
+  autoConfigCfg.append(kAutoConfigCfg.leafName);
+
+  try {
+    autoConfigJS.copyTo(kAutoConfigFile.parent, kAutoConfigFile.leafName);
+    autoConfigCfg.copyTo(kAutoConfigCfg.parent, kAutoConfigCfg.leafName);
+
+    // Make sure nsReadConfig is initialized.
+    Cc["@mozilla.org/readconfig;1"].getService(Ci.nsISupports);
+    Services.prefs.resetPrefs();
+
+    Services.obs.notifyObservers(
+      Services.prefs,
+      "prefservice:before-read-userprefs"
+    );
+
+    ok(prefs.prefHasUserValue("_autoconfig_.test.userpref-snap"));
+    equal(
+      "userpref-snap",
+      prefs.getStringPref("_autoconfig_.test.userpref-snap")
+    );
+
+    Services.prefs.resetPrefs();
+  } finally {
+    ensureRemove(kAutoConfigFile);
+    ensureRemove(kAutoConfigCfg);
+    Services.prefs.resetPrefs();
+  }
+}
diff --git a/extensions/pref/autoconfig/test/unit/xpcshell.ini b/extensions/pref/autoconfig/test/unit/xpcshell.ini
index cf9235ba8893..4db81966f47e 100644
--- a/extensions/pref/autoconfig/test/unit/xpcshell.ini
+++ b/extensions/pref/autoconfig/test/unit/xpcshell.ini
@@ -15,3 +15,7 @@ support-files =
 run-sequentially = very high failure rate in parallel
 [test_autoconfig_no_sandbox.js]
 run-sequentially = very high failure rate in parallel
+[test_autoconfig_default_path.js]
+run-if = os == 'linux'
+[test_autoconfig_custom_path.js]
+run-if = os == 'linux'
diff --git a/extensions/pref/autoconfig/test/unit/xpcshell_snap.ini b/extensions/pref/autoconfig/test/unit/xpcshell_snap.ini
new file mode 100644
index 000000000000..ff24d466460b
--- /dev/null
+++ b/extensions/pref/autoconfig/test/unit/xpcshell_snap.ini
@@ -0,0 +1,8 @@
+[DEFAULT]
+head =
+skip-if = os != 'linux'
+
+[test_autoconfig_snap.js]
+support-files =
+  autoconfig_snap.js
+  autoconfig-snap.cfg
diff --git a/modules/libpref/Preferences.cpp b/modules/libpref/Preferences.cpp
index 338a54cc7c6f..f963bbbd74ab 100644
--- a/modules/libpref/Preferences.cpp
+++ b/modules/libpref/Preferences.cpp
@@ -107,6 +107,10 @@
 #  include "windows.h"
 #endif
 
+#if defined(MOZ_WIDGET_GTK)
+#  include "mozilla/WidgetUtilsGtk.h"
+#endif  // defined(MOZ_WIDGET_GTK)
+
 using namespace mozilla;
 
 using ipc::FileDescriptor;
@@ -4860,6 +4864,23 @@ nsresult Preferences::InitInitialObjects(bool aIsStartup) {
     NS_WARNING("Error parsing application default preferences.");
   }
 
+#if defined(MOZ_WIDGET_GTK)
+  // Under Flatpak/Snap package, load /etc/firefox/defaults/pref/*.js.
+  if (mozilla::widget::IsRunningUnderFlatpakOrSnap()) {
+    nsCOMPtr<nsIFile> defaultSnapPrefDir;
+    rv = NS_GetSpecialDirectory(NS_OS_SYSTEM_CONFIG_DIR,
+                                getter_AddRefs(defaultSnapPrefDir));
+    NS_ENSURE_SUCCESS(rv, rv);
+    defaultSnapPrefDir->AppendNative("defaults"_ns);
+    defaultSnapPrefDir->AppendNative("pref"_ns);
+
+    rv = pref_LoadPrefsInDir(defaultSnapPrefDir, nullptr, 0);
+    if (NS_FAILED(rv)) {
+      NS_WARNING("Error parsing application default preferences under Snap.");
+    }
+  }
+#endif
+
   // Load jar:$app/omni.jar!/defaults/preferences/*.js
   // or jar:$gre/omni.jar!/defaults/preferences/*.js.
   RefPtr<nsZipArchive> appJarReader = Omnijar::GetReader(Omnijar::APP);
diff --git a/toolkit/components/enterprisepolicies/EnterprisePoliciesParent.sys.mjs b/toolkit/components/enterprisepolicies/EnterprisePoliciesParent.sys.mjs
index 015c4250b50b..b873f4a25693 100644
--- a/toolkit/components/enterprisepolicies/EnterprisePoliciesParent.sys.mjs
+++ b/toolkit/components/enterprisepolicies/EnterprisePoliciesParent.sys.mjs
@@ -532,12 +532,8 @@ class JSONPoliciesProvider {
     let configFile = null;
 
     if (AppConstants.platform == "linux" && AppConstants.MOZ_SYSTEM_POLICIES) {
-      let systemConfigFile = Cc["@mozilla.org/file/local;1"].createInstance(
-        Ci.nsIFile
-      );
-      systemConfigFile.initWithPath(
-        "/etc/" + Services.appinfo.name.toLowerCase() + "/policies"
-      );
+      let systemConfigFile = Services.dirsvc.get("SysConfD", Ci.nsIFile);
+      systemConfigFile.append("policies");
       systemConfigFile.append(POLICIES_FILENAME);
       if (systemConfigFile.exists()) {
         return systemConfigFile;
diff --git a/xpcom/ds/StaticAtoms.py b/xpcom/ds/StaticAtoms.py
index 473135999fc7..59d706122bc5 100644
--- a/xpcom/ds/StaticAtoms.py
+++ b/xpcom/ds/StaticAtoms.py
@@ -2447,6 +2447,7 @@ STATIC_ATOMS = [
     Atom("DirectoryService_OS_TemporaryDirectory", "TmpD"),
     Atom("DirectoryService_OS_CurrentProcessDirectory", "CurProcD"),
     Atom("DirectoryService_OS_CurrentWorkingDirectory", "CurWorkD"),
+    Atom("DirectoryService_OS_SystemConfigDir", "SysConfD"),
     # Atom("DirectoryService_OS_HomeDirectory", "Home"),  # "Home" is present above
     Atom("DirectoryService_OS_DesktopDirectory", "Desk"),
     Atom("DirectoryService_InitCurrentProcess_dummy", "MozBinD"),
diff --git a/xpcom/io/SpecialSystemDirectory.cpp b/xpcom/io/SpecialSystemDirectory.cpp
index b5373510860b..117094a690d6 100644
--- a/xpcom/io/SpecialSystemDirectory.cpp
+++ b/xpcom/io/SpecialSystemDirectory.cpp
@@ -7,6 +7,7 @@
 #include "SpecialSystemDirectory.h"
 #include "nsString.h"
 #include "nsDependentString.h"
+#include "nsIXULAppInfo.h"
 
 #if defined(XP_WIN)
 
@@ -185,6 +186,37 @@ static nsresult GetUnixHomeDir(nsIFile** aFile) {
 #  endif
 }
 
+static nsresult GetUnixSystemConfigDir(nsIFile** aFile) {
+#  if defined(ANDROID)
+  return NS_ERROR_FAILURE;
+#  else
+  nsCOMPtr<nsIXULAppInfo> appInfo =
+      do_GetService("@mozilla.org/xre/app-info;1");
+  if (!appInfo) {
+    MOZ_CRASH("No appInfo");
+  }
+
+  nsAutoCString appName;
+  nsresult rv = appInfo->GetName(appName);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  ToLowerCase(appName);
+
+  const char* mozSystemConfigDir = PR_GetEnv("MOZ_SYSTEM_CONFIG_DIR");
+  const char* defaultSystemConfigDir = "/etc";
+  nsDependentCString sysConfigDir = nsDependentCString(
+      mozSystemConfigDir ? mozSystemConfigDir : defaultSystemConfigDir);
+
+  rv = NS_NewNativeLocalFile(sysConfigDir, true, aFile);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  (*aFile)->AppendNative(appName);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return rv;
+#  endif
+}
+
 /*
   The following license applies to the xdg_user_dir_lookup function:
 
@@ -634,6 +666,9 @@ nsresult GetSpecialSystemDirectory(SystemDirectories aSystemSystemDirectory,
     case Unix_XDG_Desktop:
     case Unix_XDG_Download:
       return GetUnixXDGUserDirectory(aSystemSystemDirectory, aFile);
+
+    case Unix_SystemConfigDirectory:
+      return GetUnixSystemConfigDir(aFile);
 #endif
 
     default:
diff --git a/xpcom/io/SpecialSystemDirectory.h b/xpcom/io/SpecialSystemDirectory.h
index 167b80632cd1..8062c7549c55 100644
--- a/xpcom/io/SpecialSystemDirectory.h
+++ b/xpcom/io/SpecialSystemDirectory.h
@@ -50,7 +50,8 @@ enum SystemDirectories {
 
   Unix_HomeDirectory = 303,
   Unix_XDG_Desktop = 304,
-  Unix_XDG_Download = 306
+  Unix_XDG_Download = 306,
+  Unix_SystemConfigDirectory = 307
 };
 
 nsresult GetSpecialSystemDirectory(SystemDirectories aSystemSystemDirectory,
diff --git a/xpcom/io/nsDirectoryService.cpp b/xpcom/io/nsDirectoryService.cpp
index 679344ed35a7..9df030674917 100644
--- a/xpcom/io/nsDirectoryService.cpp
+++ b/xpcom/io/nsDirectoryService.cpp
@@ -442,6 +442,9 @@ nsDirectoryService::GetFile(const char* aProp, bool* aPersistent,
     rv =
         GetSpecialSystemDirectory(Unix_XDG_Download, getter_AddRefs(localFile));
     *aPersistent = false;
+  } else if (inAtom == nsGkAtoms::DirectoryService_OS_SystemConfigDir) {
+    rv = GetSpecialSystemDirectory(Unix_SystemConfigDirectory,
+                                   getter_AddRefs(localFile));
   }
 #endif
 
diff --git a/xpcom/io/nsDirectoryServiceDefs.h b/xpcom/io/nsDirectoryServiceDefs.h
index 8d0d2e20059f..c02b9c39e0a0 100644
--- a/xpcom/io/nsDirectoryServiceDefs.h
+++ b/xpcom/io/nsDirectoryServiceDefs.h
@@ -93,4 +93,8 @@
 #  define NS_UNIX_HOME_DIR NS_OS_HOME_DIR
 #endif
 
+#if defined(MOZ_WIDGET_GTK)
+#  define NS_OS_SYSTEM_CONFIG_DIR "SysConfD"
+#endif  // defined(MOZ_WIDGET_GTK)
+
 #endif