diff --git a/admin/configure.php b/admin/configure.php
index a7fd6e86..6d8c9044 100644
--- a/admin/configure.php
+++ b/admin/configure.php
@@ -53,7 +53,8 @@ function civicrm_setup() {
     }
 
     $extractdir = $adminPath;
-    JArchive::extract($archivename, $extractdir);
+    $archive = new Joomla\Archive\Archive;
+    $archive->extract($archivename, $extractdir);
   }
 
   $scratchDir = JPATH_SITE . DIRECTORY_SEPARATOR . 'media' . DIRECTORY_SEPARATOR . 'civicrm';
@@ -173,7 +174,7 @@ function civicrm_source($fileName, $lineMode = FALSE) {
   }
 
   if (!$lineMode) {
-    $string = JFile::read($fileName);
+    $string = file_get_contents($fileName);
 
     //get rid of comments starting with # and --
     $string = preg_replace("/^#[^\n]*$/m", "\n", $string);
@@ -233,7 +234,7 @@ function civicrm_config($frontend = FALSE, $siteKey) {
     $params['baseURL'] = $liveSite . '/';
   }
 
-  $str = JFile::read($adminPath . DIRECTORY_SEPARATOR .
+  $str = file_get_contents($adminPath . DIRECTORY_SEPARATOR .
     'civicrm' . DIRECTORY_SEPARATOR .
     'templates' . DIRECTORY_SEPARATOR .
     'CRM' . DIRECTORY_SEPARATOR .
diff --git a/admin/plugins/civicrm/civicrm.php b/admin/plugins/civicrm/civicrm.php
index e404e3a1..751bd94d 100755
--- a/admin/plugins/civicrm/civicrm.php
+++ b/admin/plugins/civicrm/civicrm.php
@@ -85,8 +85,7 @@ function onUserAfterDelete($user, $succes, $msg) {
    * @since    1.6
    */
   public function onUserLogin($user, $options = array()) {
-    $app  = JFactory::getApplication();
-    if ($app->isAdmin()) {
+    if (self::isAdminBackend()) {
       $jUser = JFactory::getUser();
       $jId = $jUser->get('id');
       self::civicrmResetNavigation($jId);
@@ -125,4 +124,27 @@ public function civicrmResetNavigation($jId = NULL) {
     CRM_Core_BAO_Navigation::resetNavigation($cId);
   }
 
+  /**
+   * Determine if we are in the Joomla administrator backend
+   *
+   * @return boolean True if in the Joomla Administrator backend otherwise false
+   */
+  private function isAdminBackend() {
+    $app = JFactory::getApplication();
+
+    // Determine if we are in the Joomla administrator backend
+    // In Joomla 3.7+ the isClient() method is used. In earlier versions use the isAdmin() method (deprecated in Joomla 4.0).
+    if (method_exists($app, 'isClient')) {
+      $isAdmin = $app->isClient('administrator');
+    }
+    elseif (method_exists($app, 'isAdmin')) {
+      $isAdmin = $app->isAdmin();
+    }
+    else {
+      throw new RuntimeException("CiviCRM User Plugin error: no method found to determine Joomla client interface.");
+    }
+
+    return $isAdmin;
+  }
+
 }
diff --git a/script.civicrm.php b/script.civicrm.php
index 8c8be863..c25d5bbf 100644
--- a/script.civicrm.php
+++ b/script.civicrm.php
@@ -83,8 +83,21 @@ function install($parent) {
   </center>';
     }
 
-    //install and enable plugins
-    $manifest  = $parent->get("manifest");
+    // Install and enable plugins
+
+    // Get the installer manifest. Use the getManifest() method if it exists (Joomla 3.4+)
+    // If not then use get("manifest") (deprecated in Joomla 4.0).
+    if (method_exists($parent, 'getManifest')) {
+      $manifest = $parent->getManifest();
+    }
+    elseif (method_exists($parent, 'get')) {
+      $manifest = $parent->get("manifest");
+    }
+    else {
+      echo "No method found to get Joomla installer manifest.";
+      exit();
+    }
+
     $parent    = $parent->getParent();
     $source    = $parent->getPath("source");
     $installer = new JInstaller();
@@ -130,7 +143,7 @@ function install($parent) {
 WHERE  $columnElement IN ($plgList)
 AND    $columnType = 'plugin'
 ");
-    $db->query();
+    $db->execute();
 
     echo $content;
   }
@@ -179,7 +192,6 @@ function setDefaultPermissions() {
     $db->setQuery('SELECT rules FROM #__assets WHERE name = ' . $db->quote('com_civicrm'));
     $assetRules = json_decode((string ) $db->loadResult());
 
-
     if (count($assetRules) > 1) {
       return;
     }
@@ -268,7 +280,7 @@ function setDefaultPermissions() {
       ' WHERE name = ' .
       $db->quote('com_civicrm')
     );
-    if (!$db->query()) {
+    if (!$db->execute()) {
       echo 'Seems like setting default actions failed<p>';
     }
   }