diff --git a/src/calibre/gui2/viewer/web_view.py b/src/calibre/gui2/viewer/web_view.py
index a8f3d828b5..fc377d7340 100644
--- a/src/calibre/gui2/viewer/web_view.py
+++ b/src/calibre/gui2/viewer/web_view.py
@@ -33,6 +33,7 @@ from calibre.gui2.webengine import (
 from calibre.srv.code import get_translations_data
 from calibre.utils.config import JSONConfig
 from calibre.utils.serialize import json_loads
+from calibre.utils.shared_file import share_open
 from polyglot.builtins import as_bytes, iteritems
 
 try:
@@ -75,7 +76,7 @@ def get_data(name):
     if path is None:
         return None, None
     try:
-        with lopen(path, 'rb') as f:
+        with share_open(path, 'rb') as f:
             return f.read(), guess_type(name)
     except EnvironmentError as err:
         prints('Failed to read from book file: {} with error: {}'.format(name, as_unicode(err)))
@@ -235,6 +236,7 @@ def create_profile():
 class ViewerBridge(Bridge):
 
     view_created = from_js(object)
+    content_file_changed = from_js(object)
     set_session_data = from_js(object, object)
     set_local_storage = from_js(object, object)
     reload_book = from_js()
@@ -437,7 +439,7 @@ class WebView(RestartingWebEngineView):
         self._host_widget = None
         self.callback_id_counter = count()
         self.callback_map = {}
-        self.current_cfi = None
+        self.current_cfi = self.current_content_file = None
         RestartingWebEngineView.__init__(self, parent)
         self.dead_renderer_error_shown = False
         self.render_process_failed.connect(self.render_process_died)
@@ -448,6 +450,7 @@ class WebView(RestartingWebEngineView):
         self._page = WebPage(self)
         self.bridge.bridge_ready.connect(self.on_bridge_ready)
         self.bridge.view_created.connect(self.on_view_created)
+        self.bridge.content_file_changed.connect(self.on_content_file_created)
         self.bridge.set_session_data.connect(self.set_session_data)
         self.bridge.set_local_storage.connect(self.set_local_storage)
         self.bridge.reload_book.connect(self.reload_book)
@@ -556,6 +559,9 @@ class WebView(RestartingWebEngineView):
     def on_view_created(self, data):
         self.view_created.emit(data)
 
+    def on_content_file_created(self, data):
+        self.current_content_file = data
+
     def start_book_load(self, initial_position=None):
         key = (set_book_path.path,)
         self.execute_when_ready('start_book_load', key, initial_position, set_book_path.pathtoebook)
diff --git a/src/pyj/read_book/view.pyj b/src/pyj/read_book/view.pyj
index c7dec0a697..c38cbc1fe1 100644
--- a/src/pyj/read_book/view.pyj
+++ b/src/pyj/read_book/view.pyj
@@ -1035,6 +1035,8 @@ class View:
             self.book_load_started = False
             if ui_operations.clear_history:
                 ui_operations.clear_history()
+        if ui_operations.content_file_changed:
+            ui_operations.content_file_changed(self.currently_showing.name)
 
     def set_progress_frac(self, progress_frac, file_progress_frac):
         self.current_progress_frac = progress_frac or 0
diff --git a/src/pyj/viewer-main.pyj b/src/pyj/viewer-main.pyj
index 5e6f06e013..f3c4bef05a 100644
--- a/src/pyj/viewer-main.pyj
+++ b/src/pyj/viewer-main.pyj
@@ -337,6 +337,8 @@ if window is window.top:
         to_python.toggle_bookmarks()
     ui_operations.toggle_inspector = def():
         to_python.toggle_inspector()
+    ui_operations.content_file_changed = def(name):
+        to_python.content_file_changed(name)
     ui_operations.reset_interface = def():
         sd = get_session_data()
         defaults = session_defaults()