diff --git a/src/calibre/gui2/viewer2/web_view.py b/src/calibre/gui2/viewer2/web_view.py
index 070c1fd6f1..595442b1ec 100644
--- a/src/calibre/gui2/viewer2/web_view.py
+++ b/src/calibre/gui2/viewer2/web_view.py
@@ -141,7 +141,13 @@ class WebPage(QWebEnginePage):
         self.bridge = ViewerBridge(self)
 
     def javaScriptConsoleMessage(self, level, msg, linenumber, source_id):
-        prints('%s:%s: %s' % (source_id, linenumber, msg))
+        if level >= QWebEnginePage.ErrorMessageLevel and source_id == 'userscript:viewer.js':
+            error_dialog(self.parent(), _('Unhandled error'), _(
+                'There was an unhandled error: {} at line: {} of {}').format(
+                    msg, linenumber, source_id.partition(':')[2]), show=True)
+        prefix = {QWebEnginePage.InfoMessageLevel: 'INFO', QWebEnginePage.WarningMessageLevel: 'WARNING'}.get(
+                level, 'ERROR')
+        prints('%s: %s:%s: %s' % (prefix, source_id, linenumber, msg))
 
     def acceptNavigationRequest(self, url, req_type, is_main_frame):
         if req_type == self.NavigationTypeReload:
diff --git a/src/pyj/viewer-main.pyj b/src/pyj/viewer-main.pyj
index ffe5195d80..914653cb5a 100644
--- a/src/pyj/viewer-main.pyj
+++ b/src/pyj/viewer-main.pyj
@@ -9,7 +9,7 @@ from gettext import gettext as _
 import initialize  # noqa: unused-import
 from ajax import ajax
 from book_list.globals import set_session_data
-from modals import error_dialog
+from modals import error_dialog, create_modal_container
 from qt import from_python, to_python
 from read_book.db import new_book
 from read_book.globals import runtime, ui_operations
@@ -45,12 +45,13 @@ def manifest_received(key, end_type, xhr, ev):
     nonlocal book
     if end_type is 'load':
         book = new_book(key, {})
-        book.manifest = xhr.response
+        book.manifest = JSON.parse(xhr.responseText)
         book.metadata = book.manifest.metadata
         book.stored_files = {}
         book.is_complete = True
         v'delete book.manifest["metadata"]'
         v'delete book.manifest["last_read_positions"]'
+        view.display_book(book)
     else:
         error_dialog(_('Could not open book'), _(
             'Failed to load book manifest, click "Show details" for more info'),
@@ -99,23 +100,16 @@ def start_book_load(key, prefs):
 
 
 def onerror(msg, script_url, line_number, column_number, error_object):
-    if error_object is None:
-        # This happens for cross-domain errors (probably javascript injected
-        # into the browser via extensions/ userscripts and the like). It also
-        # happens all the time when using Chrom on Safari, so ignore this
-        # type of error
-        console.log(f'Unhandled error from external javascript, ignoring: {msg} {script_url} {line_number}')
-        return
+    if not error_object:
+        # cross domain error
+        return False
+    fname = script_url.rpartition('/')[-1] or script_url
+    msg += '<br><span style="font-size:smaller">' + 'Error at {}:{}:{}'.format(fname, line_number, column_number or '') + '</span>'
+    details = ''
     console.log(error_object)
-    try:
-        fname = script_url.rpartition('/')[-1] or script_url
-        msg = msg + '<br><span style="font-size:smaller">' + 'Error at {}:{}:{}'.format(fname, line_number, column_number or '') + '</span>'
-        details = ''
-        details = traceback.format_exception(error_object).join('')
-        error_dialog(_('Unhandled error'), msg, details)
-        return True
-    except:
-        console.log('There was an error in the unhandled exception handler')
+    details = traceback.format_exception(error_object).join('')
+    error_dialog(_('Unhandled error'), msg, details)
+    return True
 
 
 if window is window.top:
@@ -126,6 +120,7 @@ if window is window.top:
     ui_operations.show_error = show_error
     document.body.appendChild(E.div(id='view'))
     window.onerror = onerror
+    create_modal_container()
 else:
     # iframe
     pass