MOBI Output: Add option in Preferences->Output Options->MOBI Output to enable the share via Facebook feature for calibre produced MOBI files. Note that enabling this disables the sync last read position across multiple devices feature. Don't ask me why, ask Amazon.

src/calibre/ebooks/metadata/mobi.py

@@ -330,9 +330,11 @@ class MetadataUpdater(object):
             prefs = load_defaults('mobi_output')
             pas = prefs.get('prefer_author_sort', False)
             kindle_pdoc = prefs.get('personal_doc', None)
+            share_not_sync = prefs.get('share_not_sync', False)
         except:
             pas = False
             kindle_pdoc = None
+            share_not_sync = False
         if mi.author_sort and pas:
             authors = mi.author_sort
             update_exth_record((100, normalize(authors).encode(self.codec, 'replace')))
@@ -376,7 +378,7 @@ class MetadataUpdater(object):
         # Add a 113 record if not present to allow Amazon syncing
         if (113 not in self.original_exth_records and
                 self.original_exth_records.get(501, None) == 'EBOK' and
-                not added_501):
+                not added_501 and not share_not_sync):
             from uuid import uuid4
             update_exth_record((113, str(uuid4())))
         if 503 in self.original_exth_records:

src/calibre/ebooks/mobi/output.py

@@ -55,6 +55,11 @@ class MOBIOutput(OutputFormatPlugin):
                 ' specified directory. If the directory already '
                 'exists, it will be deleted.')
         ),
+        OptionRecommendation(name='share_not_sync', recommended_value=False,
+            help=_('Enable sharing of book content via Facebook etc. '
+                ' on the Kindle. WARNING: Using this feature means that '
+                ' the book will not auto sync its last read position '
+                ' on multiple devices. Complain to Amazon.'))
     ])
 
     def check_for_periodical(self):

src/calibre/ebooks/mobi/writer2/main.py

@@ -529,9 +529,10 @@ class MobiWriter(object):
 
         if isinstance(uuid, unicode):
             uuid = uuid.encode('utf-8')
-        exth.write(pack(b'>II', 113, len(uuid) + 8))
+        if not self.opts.share_not_sync:
-        exth.write(uuid)
+            exth.write(pack(b'>II', 113, len(uuid) + 8))
-        nrecs += 1
+            exth.write(uuid)
+            nrecs += 1
 
         # Write cdetype
         if not self.is_periodical:

src/calibre/gui2/convert/mobi_output.py

@@ -23,7 +23,7 @@ class PluginWidget(Widget, Ui_Form):
         Widget.__init__(self, parent,
                 ['prefer_author_sort', 'rescale_images', 'toc_title',
                     'mobi_ignore_margins', 'mobi_toc_at_start',
-                'dont_compress', 'no_inline_toc',
+                'dont_compress', 'no_inline_toc', 'share_not_sync',
                 'personal_doc']#, 'mobi_navpoints_only_deepest']
                 )
         self.db, self.book_id = db, book_id

src/calibre/gui2/convert/mobi_output.ui

@@ -75,6 +75,13 @@
         </item>
        </layout>
       </item>
+      <item>
+       <widget class="QCheckBox" name="opt_share_not_sync">
+        <property name="text">
+         <string>Enable sharing of book content via Facebook, etc. WARNING: Disables last read syncing</string>
+        </property>
+       </widget>
+      </item>
       <item>
        <spacer name="verticalSpacer">
         <property name="orientation">