diff --git a/src/calibre/gui2/viewer/web_view.py b/src/calibre/gui2/viewer/web_view.py
index 7bc9371137..4dd85ebebf 100644
--- a/src/calibre/gui2/viewer/web_view.py
+++ b/src/calibre/gui2/viewer/web_view.py
@@ -19,7 +19,7 @@ from PyQt5.QtWebEngineWidgets import (
 
 from calibre import as_unicode, prints
 from calibre.constants import (
-    FAKE_HOST, FAKE_PROTOCOL, __version__, is_running_from_develop
+    FAKE_HOST, FAKE_PROTOCOL, __version__, is_running_from_develop, isosx, iswindows
 )
 from calibre.ebooks.metadata.book.base import field_metadata
 from calibre.ebooks.oeb.polish.utils import guess_type
@@ -172,7 +172,8 @@ def create_profile():
     ans = getattr(create_profile, 'ans', None)
     if ans is None:
         ans = QWebEngineProfile(QApplication.instance())
-        ua = 'calibre-viewer ' + __version__
+        osname = 'windows' if iswindows else ('macos' if isosx else 'linux')
+        ua = 'calibre-viewer {} {}'.format(__version__, osname)
         ans.setHttpUserAgent(ua)
         if is_running_from_develop:
             from calibre.utils.rapydscript import compile_viewer
diff --git a/src/pyj/read_book/view.pyj b/src/pyj/read_book/view.pyj
index 23152f1410..9e08f65582 100644
--- a/src/pyj/read_book/view.pyj
+++ b/src/pyj/read_book/view.pyj
@@ -78,7 +78,9 @@ def show_controls_help():
         div = div.nextSibling
         safe_set_inner_html(div, _('Use the <b>PageUp/PageDn</b> or <b>Arrow keys</b> to turn pages'))
         div = div.nextSibling
-        safe_set_inner_html(div, _('Press the <b>Esc</b> key or <b>right click</b> to show the viewer controls'))
+        safe_set_inner_html(div, _('Press the <b>Esc</b> key or <b>{} click</b> to show the viewer controls').format(
+            'control' if 'macos' in window.navigator.userAgent else _('right')
+        ))
         div = div.nextSibling
         safe_set_inner_html(div, _('Press any key to continue…'))
         focus()