--- a/toolkit/components/extensions/ExtensionCommon.jsm
+++ b/toolkit/components/extensions/ExtensionCommon.jsm
@@ -280,17 +280,19 @@ class BaseContext {
     if (!options.allowInheritsPrincipal) {
       flags |= ssm.DISALLOW_INHERIT_PRINCIPAL;
     }
     if (options.dontReportErrors) {
       flags |= ssm.DONT_REPORT_ERRORS;
     }
 
     try {
-      ssm.checkLoadURIStrWithPrincipal(this.principal, url, flags);
+      ssm.checkLoadURIWithPrincipal(this.principal,
+                                    Services.io.newURI(url),
+                                    flags);
     } catch (e) {
       return false;
     }
     return true;
   }
 
   /**
    * Safely call JSON.stringify() on an object that comes from an

--- a/toolkit/components/extensions/ExtensionParent.jsm
+++ b/toolkit/components/extensions/ExtensionParent.jsm
@@ -1321,18 +1321,18 @@ let IconDetails = {
 
     return result;
   },
 
   // Checks if the extension is allowed to load the given URL with the specified principal.
   // This will throw an error if the URL is not allowed.
   _checkURL(url, principal) {
     try {
-      Services.scriptSecurityManager.checkLoadURIStrWithPrincipal(
-        principal, url,
+      Services.scriptSecurityManager.checkLoadURIWithPrincipal(
+        principal, Services.io.newURI(url),
         Services.scriptSecurityManager.DISALLOW_SCRIPT);
     } catch (e) {
       throw new ExtensionError(`Illegal URL ${url}`);
     }
   },
 
   // Returns the appropriate icon URL for the given icons object and the
   // screen resolution of the given window.

--- a/toolkit/components/extensions/Schemas.jsm
+++ b/toolkit/components/extensions/Schemas.jsm
@@ -341,18 +341,19 @@ class Context {
    * Checks whether `url` may be loaded by the extension in this context.
    *
    * @param {string} url The URL that the extension wished to load.
    * @returns {boolean} Whether the context may load `url`.
    */
   checkLoadURL(url) {
     let ssm = Services.scriptSecurityManager;
     try {
-      ssm.checkLoadURIStrWithPrincipal(this.principal, url,
-                                       ssm.DISALLOW_INHERIT_PRINCIPAL);
+      ssm.checkLoadURIWithPrincipal(this.principal,
+                                    Services.io.newURI(url),
+                                    ssm.DISALLOW_INHERIT_PRINCIPAL);
     } catch (e) {
       return false;
     }
     return true;
   }
 
   /**
    * Checks whether this context has the given permission.