--- a/toolkit/components/extensions/Extension.jsm
+++ b/toolkit/components/extensions/Extension.jsm
@@ -38,16 +38,17 @@ const Cu = Components.utils;
 const Cr = Components.results;
 
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 Cu.import("resource://gre/modules/Services.jsm");
 
 XPCOMUtils.defineLazyModuleGetters(this, {
   AddonManager: "resource://gre/modules/AddonManager.jsm",
   AddonManagerPrivate: "resource://gre/modules/AddonManager.jsm",
+  AddonSettings: "resource://gre/modules/addons/AddonSettings.jsm",
   AppConstants: "resource://gre/modules/AppConstants.jsm",
   AsyncShutdown: "resource://gre/modules/AsyncShutdown.jsm",
   ExtensionCommon: "resource://gre/modules/ExtensionCommon.jsm",
   ExtensionPermissions: "resource://gre/modules/ExtensionPermissions.jsm",
   ExtensionStorage: "resource://gre/modules/ExtensionStorage.jsm",
   ExtensionTestCommon: "resource://testing-common/ExtensionTestCommon.jsm",
   FileSource: "resource://gre/modules/L10nRegistry.jsm",
   L10nRegistry: "resource://gre/modules/L10nRegistry.jsm",
@@ -563,17 +564,17 @@ this.ExtensionData = class {
     let webAccessibleResources = [];
 
     if (this.type === "extension") {
       if (this.manifest.devtools_page) {
         permissions.add("devtools");
       }
 
       for (let perm of manifest.permissions) {
-        if (perm === "geckoProfiler") {
+        if (perm === "geckoProfiler" && !this.isPrivileged) {
           const acceptedExtensions = Services.prefs.getStringPref("extensions.geckoProfiler.acceptedExtensionIds", "");
           if (!acceptedExtensions.split(",").includes(id)) {
             this.manifestError("Only whitelisted extensions are allowed to access the geckoProfiler.");
             continue;
           }
         }
 
         let type = classifyPermission(perm);
@@ -1211,20 +1212,31 @@ this.Extension = class extends Extension
         this.localeData.messages.set(locale, result);
       });
   }
 
   get manifestCacheKey() {
     return [this.id, this.version, Services.locale.getAppLocaleAsLangTag()];
   }
 
+  get isPrivileged() {
+    return (this.addonData.signedState === AddonManager.SIGNEDSTATE_PRIVILEGED ||
+            (AppConstants.MOZ_ALLOW_LEGACY_EXTENSIONS &&
+             this.addonData.temporarilyInstalled));
+  }
+
+  get experimentsAllowed() {
+    return (AddonSettings.ALLOW_LEGACY_EXTENSIONS ||
+            this.isPrivileged);
+  }
+
   async _parseManifest() {
     let manifest = await super.parseManifest();
     if (manifest && manifest.permissions.has("mozillaAddons") &&
-        this.addonData.signedState !== AddonManager.SIGNEDSTATE_PRIVILEGED) {
+        !this.isPrivileged) {
       Cu.reportError(`Stripping mozillaAddons permission from ${this.id}`);
       manifest.permissions.delete("mozillaAddons");
       let i = manifest.manifest.permissions.indexOf("mozillaAddons");
       if (i >= 0) {
         manifest.manifest.permissions.splice(i, 1);
       } else {
         throw new Error("Could not find mozilaAddons in original permissions array");
       }

--- a/toolkit/mozapps/extensions/internal/XPIProvider.jsm
+++ b/toolkit/mozapps/extensions/internal/XPIProvider.jsm
@@ -4378,16 +4378,17 @@ this.XPIProvider = {
       }
 
       let params = {
         id: aAddon.id,
         version: aAddon.version,
         installPath: aFile.clone(),
         resourceURI: getURIForResourceInFile(aFile, ""),
         signedState: aAddon.signedState,
+        temporarilyInstalled: aAddon._installLocation == TemporaryInstallLocation,
       };
 
       if (aMethod == "startup" && aAddon.startupData) {
         params.startupData = aAddon.startupData;
       }
 
       if (aExtraParams) {
         for (let key in aExtraParams) {