diff --git a/src/calibre/constants.py b/src/calibre/constants.py
index 75e6b28095..7be575a121 100644
--- a/src/calibre/constants.py
+++ b/src/calibre/constants.py
@@ -334,7 +334,7 @@ if cconfd is not None:
 elif iswindows:
     from calibre_extensions import winutil
     try:
-        config_dir = winutil.special_folder_path(plugins['winutil'][0].CSIDL_APPDATA)
+        config_dir = winutil.special_folder_path(winutil.CSIDL_APPDATA)
     except ValueError:
         config_dir = None
     if not config_dir or not os.access(config_dir, os.W_OK|os.X_OK):
diff --git a/src/calibre/debug.py b/src/calibre/debug.py
index 412b42facf..ddc3fb7879 100644
--- a/src/calibre/debug.py
+++ b/src/calibre/debug.py
@@ -182,14 +182,15 @@ def print_basic_debug_info(out=None):
     import platform
     from contextlib import suppress
     from calibre.constants import (__appname__, get_version, isportable, ismacos,
-                                   isfrozen, is64bit, plugins)
+                                   isfrozen, is64bit)
     from calibre.utils.localization import set_translators
     out(__appname__, get_version(), 'Portable' if isportable else '',
         'embedded-python:', isfrozen, 'is64bit:', is64bit)
     out(platform.platform(), platform.system(), platform.architecture())
     if iswindows and not is64bit:
+        from calibre_extensions.winutil import is_wow64_process
         with suppress(Exception):
-            if plugins['winutil'][0].is_wow64_process():
+            if is_wow64_process():
                 out('32bit process running on 64bit windows')
     out(platform.system_alias(platform.system(), platform.release(),
             platform.version()))
diff --git a/src/calibre/devices/kindle/bookmark.py b/src/calibre/devices/kindle/bookmark.py
index c0811fefe2..fb135a688f 100644
--- a/src/calibre/devices/kindle/bookmark.py
+++ b/src/calibre/devices/kindle/bookmark.py
@@ -305,13 +305,6 @@ class Bookmark():  # {{{
                     self.book_length = mu.book_length
             except:
                 pass
-        elif self.bookmark_extension == 'pdr':
-            from calibre.constants import plugins
-            try:
-                self.book_length = plugins['pdfreflow'][0].get_numpages(open(book_fs).read())
-            except :
-                pass
-
         else:
             print("unsupported bookmark_extension: %s" % self.bookmark_extension)
 
diff --git a/src/calibre/devices/kobo/driver.py b/src/calibre/devices/kobo/driver.py
index f4dd6127d3..953182f50e 100644
--- a/src/calibre/devices/kobo/driver.py
+++ b/src/calibre/devices/kobo/driver.py
@@ -1524,9 +1524,8 @@ class KOBOTOUCH(KOBO):
         # Wrap some debugging output in a try/except so that it is unlikely to break things completely.
         try:
             if DEBUG:
-                from calibre.constants import plugins
-                usbobserver, usbobserver_err = plugins['usbobserver']
-                mount_map = usbobserver.get_mounted_filesystems()
+                from calibre_extensions.usbobserver import get_mounted_filesystems
+                mount_map = get_mounted_filesystems()
                 debug_print('KoboTouch::open_osx - mount_map=', mount_map)
                 debug_print('KoboTouch::open_osx - self._main_prefix=', self._main_prefix)
                 debug_print('KoboTouch::open_osx - self._card_a_prefix=', self._card_a_prefix)
diff --git a/src/calibre/devices/mtp/windows/driver.py b/src/calibre/devices/mtp/windows/driver.py
index 712f895248..1bb06f6e9f 100644
--- a/src/calibre/devices/mtp/windows/driver.py
+++ b/src/calibre/devices/mtp/windows/driver.py
@@ -12,7 +12,7 @@ from polyglot.builtins import iteritems, itervalues, unicode_type, zip
 from itertools import chain
 
 from calibre import as_unicode, prints, force_unicode
-from calibre.constants import plugins, __appname__, numeric_version, isxp
+from calibre.constants import __appname__, numeric_version, isxp
 from calibre.ptempfile import SpooledTemporaryFile
 from calibre.devices.errors import OpenFailed, DeviceError, BlacklistedDevice
 from calibre.devices.mtp.base import MTPDeviceBase, debug
@@ -63,7 +63,12 @@ class MTP_DEVICE(MTPDeviceBase):
             self.wpd = None
             self.wpd_error = _('MTP devices are not supported on Windows XP')
         else:
-            self.wpd, self.wpd_error = plugins['wpd']
+            try:
+                from calibre_extensions import wpd
+                self.wpd = wpd
+            except Exception as err:
+                self.wpd = None
+                self.wpd_error = as_unicode(err)
         if self.wpd is not None:
             try:
                 self.wpd.init(__appname__, *(numeric_version[:3]))
diff --git a/src/calibre/devices/mtp/windows/remote.py b/src/calibre/devices/mtp/windows/remote.py
index 2bbe8ae766..265b0423b2 100644
--- a/src/calibre/devices/mtp/windows/remote.py
+++ b/src/calibre/devices/mtp/windows/remote.py
@@ -6,7 +6,7 @@ __license__   = 'GPL v3'
 __copyright__ = '2012, Kovid Goyal <kovid at kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
-import subprocess, sys, os, pprint, signal, time, glob, io
+import subprocess, os, pprint, signal, time, glob, io
 pprint, io
 from polyglot.builtins import environ_item
 
@@ -48,14 +48,6 @@ def main():
         subprocess.call(['calibre-debug', '-e', fp], env=env)
         return
 
-    sys.path.insert(0, os.path.dirname(fp))
-    if 'wpd' in sys.modules:
-        del sys.modules['wpd']
-    import wpd
-    from calibre.constants import plugins
-    plugins._plugins['wpd'] = (wpd, '')
-    sys.path.pop(0)
-
     # from calibre.devices.mtp.test import run
     # run()
     # return
diff --git a/src/calibre/devices/scanner.py b/src/calibre/devices/scanner.py
index 4088f256be..5b62d2e68c 100644
--- a/src/calibre/devices/scanner.py
+++ b/src/calibre/devices/scanner.py
@@ -11,7 +11,7 @@ from collections import namedtuple
 from threading import Lock
 
 from calibre import prints, as_unicode
-from calibre.constants import (iswindows, ismacos, plugins, islinux, isfreebsd,
+from calibre.constants import (iswindows, ismacos, islinux, isfreebsd,
         isnetbsd)
 from polyglot.builtins import range
 
@@ -60,11 +60,8 @@ class LibUSBScanner(object):
 
     def __call__(self):
         if not hasattr(self, 'libusb'):
-            self.libusb, self.libusb_err = plugins['libusb']
-            if self.libusb is None:
-                raise ValueError(
-                    'DeviceScanner needs libusb to work. Error: %s'%
-                    self.libusb_err)
+            from calibre_extensions import libusb
+            self.libusb = libusb
 
         ans = set()
         seen = set()
@@ -172,16 +169,6 @@ if islinux:
     linux_scanner = LinuxScanner()
 
 libusb_scanner = LibUSBScanner()
-if False and ismacos:
-    # Apparently libusb causes mem leaks on some Macs and hangs on others and
-    # works on a few. OS X users will just have to live without MTP support.
-    # See https://bugs.launchpad.net/calibre/+bug/1044706
-    # See https://bugs.launchpad.net/calibre/+bug/1044758
-    # osx_scanner = libusb_scanner
-    usbobserver, usbobserver_err = plugins['usbobserver']
-    if usbobserver is None:
-        raise RuntimeError('Failed to load usbobserver: %s'%usbobserver_err)
-    osx_scanner = usbobserver.get_usb_devices
 
 if isfreebsd:
     freebsd_scanner = libusb_scanner
diff --git a/src/calibre/devices/usbms/device.py b/src/calibre/devices/usbms/device.py
index 98cb16104d..fae4edc465 100644
--- a/src/calibre/devices/usbms/device.py
+++ b/src/calibre/devices/usbms/device.py
@@ -21,12 +21,11 @@ from calibre.constants import DEBUG
 from calibre.devices.interface import DevicePlugin
 from calibre.devices.errors import DeviceError
 from calibre.devices.usbms.deviceconfig import DeviceConfig
-from calibre.constants import iswindows, islinux, ismacos, isfreebsd, plugins
+from calibre.constants import iswindows, islinux, ismacos, isfreebsd
 from calibre.utils.filenames import ascii_filename as sanitize
 from polyglot.builtins import iteritems, string_or_bytes, map
 
 if ismacos:
-    usbobserver, usbobserver_err = plugins['usbobserver']
     osx_sanitize_name_pat = re.compile(r'[.-]')
 
 if iswindows:
@@ -314,9 +313,8 @@ class Device(DeviceConfig, DevicePlugin):
 
     @classmethod
     def osx_get_usb_drives(cls):
-        if usbobserver_err:
-            raise RuntimeError('Failed to load usbobserver: '+usbobserver_err)
-        return usbobserver.get_usb_drives()
+        from calibre_extensions.usbobserver import get_usb_drives
+        return get_usb_drives()
 
     def _osx_bsd_names(self):
         drives = self.osx_get_usb_drives()
@@ -390,9 +388,10 @@ class Device(DeviceConfig, DevicePlugin):
         return drives
 
     def open_osx(self):
+        from calibre_extensions.usbobserver import get_mounted_filesystems
         bsd_drives = self.osx_bsd_names()
         drives = self.osx_sort_names(bsd_drives.copy())
-        mount_map = usbobserver.get_mounted_filesystems()
+        mount_map = get_mounted_filesystems()
         drives = {k: mount_map.get(v) for k, v in iteritems(drives)}
         if DEBUG:
             print()
diff --git a/src/calibre/gui_launch.py b/src/calibre/gui_launch.py
index 320460ae3c..6e2bdc4e1a 100644
--- a/src/calibre/gui_launch.py
+++ b/src/calibre/gui_launch.py
@@ -25,8 +25,8 @@ def do_detach(fork=True, setsid=True, redirect=True):
     if setsid:
         os.setsid()
     if redirect:
-        from calibre.constants import plugins
-        plugins['speedup'][0].detach(os.devnull)
+        from calibre_extensions.speedup import detach
+        detach(os.devnull)
     is_detached = True
 
 
diff --git a/src/calibre/utils/localization.py b/src/calibre/utils/localization.py
index 6874f39ca0..6b9b7754c3 100644
--- a/src/calibre/utils/localization.py
+++ b/src/calibre/utils/localization.py
@@ -29,7 +29,7 @@ def available_translations():
 
 
 def get_system_locale():
-    from calibre.constants import iswindows, ismacos, plugins
+    from calibre.constants import iswindows, ismacos
     lang = None
     if iswindows:
         try:
@@ -41,9 +41,10 @@ def get_system_locale():
         except:
             pass  # Windows XP does not have the GetUserDefaultLocaleName fn
     elif ismacos:
+        from calibre_extensions.usbobserver import user_locale
         try:
-            lang = plugins['usbobserver'][0].user_locale() or None
-        except:
+            lang = user_locale() or None
+        except Exception:
             # Fallback to environment vars if something bad happened
             import traceback
             traceback.print_exc()
diff --git a/src/calibre/utils/matcher.py b/src/calibre/utils/matcher.py
index dfca519ab7..078574db36 100644
--- a/src/calibre/utils/matcher.py
+++ b/src/calibre/utils/matcher.py
@@ -14,7 +14,7 @@ from collections import OrderedDict
 from itertools import islice
 
 from calibre import detect_ncpus as cpu_count, as_unicode
-from calibre.constants import plugins, filesystem_encoding
+from calibre.constants import filesystem_encoding
 from calibre.utils.icu import primary_sort_key, primary_find, primary_collator
 from polyglot.builtins import iteritems, itervalues, map, unicode_type, range, zip, raw_input, filter, getcwd
 from polyglot.queue import Queue
@@ -255,12 +255,8 @@ class CScorer(object):
         level2=DEFAULT_LEVEL2,
         level3=DEFAULT_LEVEL3
     ):
-        speedup, err = plugins['matcher']
-        if speedup is None:
-            raise PluginFailed(
-                'Failed to load the matcher plugin with error: %s' % err
-            )
-        self.m = speedup.Matcher(
+        from calibre_extensions.matcher import Matcher
+        self.m = Matcher(
             items,
             primary_collator().capsule,
             unicode_type(level1), unicode_type(level2), unicode_type(level3)
diff --git a/src/calibre/utils/unicode_names.py b/src/calibre/utils/unicode_names.py
index 3ef9a739df..b61c165c12 100644
--- a/src/calibre/utils/unicode_names.py
+++ b/src/calibre/utils/unicode_names.py
@@ -5,13 +5,13 @@
 
 from collections import defaultdict
 
-from calibre.constants import plugins
 from calibre.utils.icu import ord_string
 from polyglot.builtins import iteritems
 
 
 def character_name_from_code(code):
-    return plugins['unicode_names'][0].name_for_codepoint(code) or 'U+{:X}'.format(code)
+    from calibre_extensions.unicode_names import name_for_codepoint
+    return name_for_codepoint(code) or 'U+{:X}'.format(code)
 
 
 def html_entities():
@@ -35,7 +35,8 @@ def points_for_word(w):
     w = w.lower()
     ans = points_for_word.cache.get(w)
     if ans is None:
-        ans = plugins['unicode_names'][0].codepoints_for_word(w) | html_entities().get(w, set())
+        from calibre_extensions.unicode_names import codepoints_for_word
+        ans = codepoints_for_word(w) | html_entities().get(w, set())
         points_for_word.cache[w] = ans
     return ans
 
diff --git a/src/calibre/utils/winreg/default_programs.py b/src/calibre/utils/winreg/default_programs.py
index f15d0865e2..6e0c5f99e6 100644
--- a/src/calibre/utils/winreg/default_programs.py
+++ b/src/calibre/utils/winreg/default_programs.py
@@ -10,7 +10,7 @@ from threading import Thread
 
 
 from calibre import guess_type, prints
-from calibre.constants import is64bit, isportable, isfrozen, __version__, DEBUG, plugins
+from calibre.constants import is64bit, isportable, isfrozen, __version__, DEBUG
 from calibre.utils.winreg.lib import Key, HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE
 from calibre.utils.lock import singleinstance
 from polyglot.builtins import iteritems, itervalues
@@ -131,7 +131,6 @@ def register():
         with Key(r'Software\RegisteredApplications') as key:
             key.set(data['name'], capabilities_path)
 
-    winutil = plugins['winutil'][0]
     winutil.notify_associations_changed()
 
 
@@ -228,12 +227,12 @@ def split_commandline(commandline):
     # CommandLineToArgvW returns path to executable if called with empty string.
     if not commandline.strip():
         return []
-    return list(plugins['winutil'][0].parse_cmdline(commandline))
+    return list(winutil.parse_cmdline(commandline))
 
 
 def friendly_app_name(prog_id=None, exe=None):
     try:
-        return plugins['winutil'][0].friendly_name(prog_id, exe)
+        return winutil.friendly_name(prog_id, exe)
     except Exception:
         traceback.print_exc()