diff --git a/resources/mime.types b/resources/mime.types
index a2a67c38f9..afc5e9b849 100644
--- a/resources/mime.types
+++ b/resources/mime.types
@@ -822,7 +822,6 @@ application/x-lzh				lzh
 application/x-lzx				lzx
 application/x-maker				book fb fbdoc fm frame frm maker
 application/x-mif				mif
-application/x-mobipocket-ebook				mobi prc
 application/x-ms-application				application
 application/x-ms-wmd				wmd
 application/x-ms-wmz				wmz
@@ -1371,11 +1370,11 @@ application/x-sony-bbeb                    lrf lrx
 application/adobe-page-template+xml        xpgt
 application/x-font-opentype                otf
 application/x-font-truetype                ttf
-application/x-mobipocket-ebook             mobi prc azw
+application/x-mobipocket-ebook             mobi prc 
+application/vnd.amazon.ebook               azw3 azw azw2 azw4
 application/x-cbz                          cbz
 application/x-cbr                          cbr
 application/x-cb7                          cb7
 application/x-koboreader-ebook             kobo
 image/wmf                                  wmf
 application/ereader                        pdb
-
diff --git a/src/calibre/__init__.py b/src/calibre/__init__.py
index a0f3b49498..ac8e681fed 100644
--- a/src/calibre/__init__.py
+++ b/src/calibre/__init__.py
@@ -54,6 +54,16 @@ def guess_all_extensions(*args, **kwargs):
         _init_mimetypes()
     return mimetypes.guess_all_extensions(*args, **kwargs)
 
+
+def guess_extension(*args, **kwargs):
+    import mimetypes
+    if not _mt_inited:
+        _init_mimetypes()
+    ext = mimetypes.guess_extension(*args, **kwargs)
+    if not ext and args and args[0] == 'application/x-palmreader':
+        ext = '.pdb'
+    return ext
+
 def get_types_map():
     import mimetypes
     if not _mt_inited:
diff --git a/src/calibre/customize/builtins.py b/src/calibre/customize/builtins.py
index ee08dec71c..0427d3084b 100644
--- a/src/calibre/customize/builtins.py
+++ b/src/calibre/customize/builtins.py
@@ -1351,6 +1351,15 @@ class StoreEbookscomStore(StoreBase):
     formats = ['EPUB', 'LIT', 'MOBI', 'PDF']
     affiliate = True
 
+# class StoreEbooksGratuitsStore(StoreBase):
+#     name = 'EbooksGratuits.com'
+#     description = u''
+#     actual_plugin = 'calibre.gui2.store.stores.ebooksgratuits_plugin:EbooksGratuitsStore'
+#
+#     headquarters = 'FR'
+#     formats = ['EPUB', 'MOBI', 'PDF', 'PDB']
+#     drm_free_only = True
+#
 # class StoreEBookShoppeUKStore(StoreBase):
 #     name = 'ebookShoppe UK'
 #     author = u'Charles Haley'
@@ -1645,6 +1654,7 @@ plugins += [
     StoreEbookNLStore,
     StoreEbookpointStore,
     StoreEbookscomStore,
+    # StoreEbooksGratuitsStore,
     StoreEHarlequinStore,
     StoreEKnigiStore,
     StoreEscapeMagazineStore,
diff --git a/src/calibre/gui2/store/opensearch_store.py b/src/calibre/gui2/store/opensearch_store.py
index a66418aa77..ccba65b990 100644
--- a/src/calibre/gui2/store/opensearch_store.py
+++ b/src/calibre/gui2/store/opensearch_store.py
@@ -13,7 +13,7 @@ from lxml import etree
 
 from PyQt4.Qt import QUrl
 
-from calibre import browser
+from calibre import (browser, guess_extension)
 from calibre.gui2 import open_url
 from calibre.gui2.store import StorePlugin
 from calibre.gui2.store.search_result import SearchResult
@@ -29,7 +29,7 @@ class OpenSearchOPDSStore(StorePlugin):
     def open(self, parent=None, detail_item=None, external=False):
         if not hasattr(self, 'web_url'):
             return
-        
+
         if external or self.config.get('open_external', False):
             open_url(QUrl(detail_item if detail_item else self.web_url))
         else:
@@ -52,7 +52,7 @@ class OpenSearchOPDSStore(StorePlugin):
         oquery.searchTerms = query
         oquery.count = max_results
         url = oquery.url()
-        
+
         counter = max_results
         br = browser()
         with closing(br.open(url, timeout=timeout)) as f:
@@ -60,18 +60,18 @@ class OpenSearchOPDSStore(StorePlugin):
             for data in doc.xpath('//*[local-name() = "entry"]'):
                 if counter <= 0:
                     break
-            
+
                 counter -= 1
-    
+
                 s = SearchResult()
-                
+
                 s.detail_item = ''.join(data.xpath('./*[local-name() = "id"]/text()')).strip()
 
                 for link in data.xpath('./*[local-name() = "link"]'):
                     rel = link.get('rel')
                     href = link.get('href')
                     type = link.get('type')
-                    
+
                     if rel and href and type:
                         if 'http://opds-spec.org/thumbnail' in rel:
                             s.cover_url = href
@@ -81,15 +81,15 @@ class OpenSearchOPDSStore(StorePlugin):
                             s.detail_item = href
                         elif 'http://opds-spec.org/acquisition' in rel:
                             if type:
-                                ext = mimetypes.guess_extension(type)
+                                ext = guess_extension(type)
                                 if ext:
                                     ext = ext[1:].upper().strip()
                                     s.downloads[ext] = href
                 s.formats = ', '.join(s.downloads.keys()).strip()
-                
+
                 s.title = ' '.join(data.xpath('./*[local-name() = "title"]//text()')).strip()
                 s.author = ', '.join(data.xpath('./*[local-name() = "author"]//*[local-name() = "name"]//text()')).strip()
-                
+
                 price_e = data.xpath('.//*[local-name() = "price"][1]')
                 if price_e:
                     price_e = price_e[0]
@@ -97,6 +97,6 @@ class OpenSearchOPDSStore(StorePlugin):
                     price = ''.join(price_e.xpath('.//text()')).strip()
                     s.price = currency_code + ' ' + price
                     s.price = s.price.strip()
-                
+
 
                 yield s