diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2d36af4bda..8c1776ab09 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -26,6 +26,7 @@
 - Convert images in HTML content pasted into HTML editor to `data:` URIs (and later to attachments) (#6938)
 - Add possibility to change ATTR_EMULATE_PREPARES via config file (#9213)
 - Use draft settings (like DSN) on "Edit as new" (#9349)
+- Use new HTML5 parser available on PHP >= 8.4
 - Mailvelope: Add a button to enable the extension for webmail domain (#9498)
 - OAuth: Add support for SMTP without authentication (#9183)
 - OAuth: Add support for OAuth/OpenIDC discovery (#8201)
@@ -58,6 +59,9 @@
 - Fix attachment name decoding when 'charset' parameter exists in the headers (#9376)
 - Fix deprecated (in PHP 8.4) use of session_set_save_handler() (#9060)
 - Fix potential HTTP protocol version mismatch (#8982)
+
+## Release 1.6.9
+
 - Fix regression where printing/scaling/rotating image attachments was broken (#9571)
 - Fix regression where HTML messages were displayed unstyled (#9586)
 
diff --git a/program/lib/Roundcube/rcube_washtml.php b/program/lib/Roundcube/rcube_washtml.php
index 95a6371139..5560e890ef 100644
--- a/program/lib/Roundcube/rcube_washtml.php
+++ b/program/lib/Roundcube/rcube_washtml.php
@@ -1,5 +1,6 @@
 <?php
 
+use Dom\HTMLDocument;
 use Masterminds\HTML5;
 
 /*
@@ -299,7 +300,7 @@ private function wash_attribs($node)
 
                 // in SVG to/from attribs may contain anything, including URIs
                 if ($key == 'to' || $key == 'from') {
-                    $key = strtolower($node->getAttribute('attributeName'));
+                    $key = strtolower((string) $node->getAttribute('attributeName'));
                     if ($key && !isset($this->_html_attribs[$key])) {
                         $key = null;
                     }
@@ -328,6 +329,8 @@ private function wash_attribs($node)
                     && (in_array($key, ['id', 'class', 'for']) || ($key == 'name' && $node->nodeName == 'a'))
                 ) {
                     $out = preg_replace('/(\S+)/', $this->_css_prefix . '\1', $value);
+                } elseif ($key == 'xmlns' && !strpos($value, '://')) {
+                    continue;
                 } elseif ($key) {
                     $out = $value;
                 }
@@ -579,12 +582,22 @@ private function dumpHtml($node, $level = 20)
                             $this->wash_attribs($node), $this->dumpHtml($node, $level), $this);
                     } elseif (isset($this->_html_elements[$tagName])) {
                         $content = $this->dumpHtml($node, $level);
-                        $tag = '<' . $node->nodeName;
+                        $tag = '<' . $tagName;
 
                         if ($tagName == 'svg') {
-                            $xpath = new DOMXPath($node->ownerDocument);
-                            foreach ($xpath->query('namespace::*') as $ns) {
-                                if ($ns->nodeName != 'xmlns:xml') {
+                            if (method_exists($node, 'getInScopeNamespaces')) {
+                                $ns_nodes = $node->getInScopeNamespaces();
+                            } else {
+                                $xpath = new DOMXPath($node->ownerDocument);
+                                $ns_nodes = $xpath->query('namespace::*');
+                            }
+
+                            foreach ($ns_nodes as $ns) {
+                                if (isset($ns->nodeName) && isset($ns->nodeValue)
+                                    && $ns->nodeName != 'xmlns:xml'
+                                    && preg_match('/^[a-zA-Z:-]+$/', $ns->nodeName)
+                                    && strpos($ns->nodeValue, '://')
+                                ) {
                                     $tag .= sprintf(' %s="%s"',
                                         $ns->nodeName,
                                         htmlspecialchars($ns->nodeValue, \ENT_QUOTES, $this->config['charset'])
@@ -602,15 +615,15 @@ private function dumpHtml($node, $level = 20)
                         } elseif ($content === '' && ($this->is_xml || isset($this->_void_elements[$tagName]))) {
                             $dump .= $tag . ' />';
                         } else {
-                            $dump .= $tag . '>' . $content . '</' . $node->nodeName . '>';
+                            $dump .= $tag . '>' . $content . '</' . $tagName . '>';
                         }
                     } elseif (isset($this->_ignore_elements[$tagName])) {
                         if ($this->config['add_comments']) {
-                            $dump .= '<!-- ' . htmlspecialchars($node->nodeName, \ENT_QUOTES, $this->config['charset']) . ' not allowed -->';
+                            $dump .= '<!-- ' . htmlspecialchars($tagName, \ENT_QUOTES, $this->config['charset']) . ' not allowed -->';
                         }
                     } else {
                         if ($this->config['add_comments']) {
-                            $dump .= '<!-- ' . htmlspecialchars($node->nodeName, \ENT_QUOTES, $this->config['charset']) . ' ignored -->';
+                            $dump .= '<!-- ' . htmlspecialchars($tagName, \ENT_QUOTES, $this->config['charset']) . ' ignored -->';
                         }
                         $dump .= $this->dumpHtml($node, $level); // ignore tags not its content
                     }
@@ -657,8 +670,19 @@ public function wash($html)
         $this->is_xml = !preg_match('/<(html|head|body)/i', $html) && stripos($html, '<svg') !== false;
         $method = $this->is_xml ? 'loadXML' : 'loadHTML';
 
+        // Try HTML5 parser available in PHP >= 8.4
+        // TODO: Parse XML also with this new PHP parser (?)
+        if (!$this->is_xml && class_exists('Dom\HTMLDocument')) {
+            try {
+                $options = constant('Dom\HTML_NO_DEFAULT_NS') | \LIBXML_COMPACT | \LIBXML_NOERROR;
+                $node = HTMLDocument::createFromString($html, $options, $this->config['charset']);
+            } catch (Exception $e) {
+                // ignore, fallback to other methods
+            }
+        }
+
         // DOMDocument does not support HTML5, try Masterminds parser if available
-        if (!$this->is_xml && class_exists('Masterminds\HTML5')) {
+        if (empty($node) && !$this->is_xml && class_exists('Masterminds\HTML5')) {
             try {
                 // disabled_html_ns=true is a workaround for the performance issue
                 // https://github.com/Masterminds/html5-php/issues/181
diff --git a/tests/Framework/WashtmlTest.php b/tests/Framework/WashtmlTest.php
index 0cd49e0ca0..0117e7bf1c 100644
--- a/tests/Framework/WashtmlTest.php
+++ b/tests/Framework/WashtmlTest.php
@@ -362,7 +362,7 @@ public function test_wash_svg()
   <!-- script not allowed -->
   <text x="10" y="25">An example text</text>
   <a xlink:href="http://www.w.pl"><rect width="100%" height="100%" /></a>
-  <!-- foreignObject ignored -->
+  <!-- foreignobject ignored -->
   <set attributeName="onmouseover" x-washed="to" />
   <animate attributeName="onunload" x-washed="to" />
   <animate attributeName="xlink:href" begin="0" x-washed="from" />
@@ -400,7 +400,7 @@ public static function provide_wash_svg_tests_cases(): iterable
             ],
             [
                 '<svg xmlns="&quot; onload=&quot;alert(document.domain)" />',
-                '<svg xmlns="&quot; onload=&quot;alert(document.domain)" />',
+                '<svg />',
             ],
             [
                 '<html><svg xmlns="&quot; onload=&quot;alert(document.domain)" />',
@@ -824,23 +824,15 @@ public function test_table_bug7356()
   <tr><td></td></tr>
 </table>';
 
-        $expected = '
-<table id="t1">
-  <tr>
-    <td>
-      <table id="t2">
-        <tr>
-          <td></td>
-        </tr>
-      </table>
-    </td>
-  </tr>
-  <tr><td></td></tr>
-</table>';
+        $expected = '<table id="t1"><tr><td><table id="t2"><tr><td></td></tr></table></td></tr><tr><td></td></tr></table>';
+
+        if (class_exists('Dom\HTMLDocument')) {
+            $expected = '<table id="t1"><tbody><tr><td><table id="t2"><tbody><tr></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr></tbody></table>';
+        }
 
         $washer = new \rcube_washtml();
         $washed = $this->cleanupResult($washer->wash($html));
 
-        $this->assertSame(trim($expected), $washed);
+        $this->assertSame($expected, preg_replace('/>[^<>]+</', '><', $washed));
     }
 }