diff --git a/plugins/CuraEngineBackend/CuraEngineBackend.py b/plugins/CuraEngineBackend/CuraEngineBackend.py
index 91a9ee0e7b..58bc74f3f1 100755
--- a/plugins/CuraEngineBackend/CuraEngineBackend.py
+++ b/plugins/CuraEngineBackend/CuraEngineBackend.py
@@ -179,8 +179,7 @@ class CuraEngineBackend(QObject, Backend):
     #   This is useful for debugging and used to actually start the engine.
     #   \return list of commands and args / parameters.
     def getEngineCommand(self) -> List[str]:
-        json_path = Resources.getPath(Resources.DefinitionContainers, "fdmprinter.def.json")
-        command = [self._application.getPreferences().getValue("backend/location"), "connect", "127.0.0.1:{0}".format(self._port), "-j", json_path, ""]
+        command = [self._application.getPreferences().getValue("backend/location"), "connect", "127.0.0.1:{0}".format(self._port), ""]
 
         parser = argparse.ArgumentParser(prog = "cura", add_help = False)
         parser.add_argument("--debug", action = "store_true", default = False, help = "Turn on the debug mode by setting this option.")
diff --git a/plugins/CuraEngineBackend/StartSliceJob.py b/plugins/CuraEngineBackend/StartSliceJob.py
index 28e442033b..dd0d9db0a2 100644
--- a/plugins/CuraEngineBackend/StartSliceJob.py
+++ b/plugins/CuraEngineBackend/StartSliceJob.py
@@ -440,8 +440,7 @@ class StartSliceJob(Job):
             Job.yieldThread()
 
         # Ensure that the engine is aware what the build extruder is.
-        if stack.getProperty("machine_extruder_count", "value") > 1:
-            changed_setting_keys.add("extruder_nr")
+        changed_setting_keys.add("extruder_nr")
 
         # Get values for all changed settings
         for key in changed_setting_keys:
diff --git a/plugins/GCodeGzReader/GCodeGzReader.py b/plugins/GCodeGzReader/GCodeGzReader.py
index 73a08075d2..d075e4e3b0 100644
--- a/plugins/GCodeGzReader/GCodeGzReader.py
+++ b/plugins/GCodeGzReader/GCodeGzReader.py
@@ -4,15 +4,22 @@
 import gzip
 
 from UM.Mesh.MeshReader import MeshReader #The class we're extending/implementing.
+from UM.MimeTypeDatabase import MimeTypeDatabase, MimeType #To add the .gcode.gz files to the MIME type database.
 from UM.PluginRegistry import PluginRegistry
 
-
 ##  A file reader that reads gzipped g-code.
 #
 #   If you're zipping g-code, you might as well use gzip!
 class GCodeGzReader(MeshReader):
     def __init__(self) -> None:
         super().__init__()
+        MimeTypeDatabase.addMimeType(
+            MimeType(
+                name = "application/x-cura-compressed-gcode-file",
+                comment = "Cura Compressed GCode File",
+                suffixes = ["gcode.gz"]
+            )
+        )
         self._supported_extensions = [".gcode.gz"]
 
     def _read(self, file_name):
diff --git a/plugins/GCodeReader/GCodeReader.py b/plugins/GCodeReader/GCodeReader.py
index 45ef1e1058..1bc22a3e62 100755
--- a/plugins/GCodeReader/GCodeReader.py
+++ b/plugins/GCodeReader/GCodeReader.py
@@ -1,4 +1,5 @@
 # Copyright (c) 2017 Aleph Objects, Inc.
+# Copyright (c) 2018 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
 
 from UM.FileHandler.FileReader import FileReader
@@ -11,13 +12,7 @@ catalog = i18nCatalog("cura")
 from . import MarlinFlavorParser, RepRapFlavorParser
 
 
-MimeTypeDatabase.addMimeType(
-    MimeType(
-        name = "application/x-cura-gcode-file",
-        comment = "Cura GCode File",
-        suffixes = ["gcode", "gcode.gz"]
-    )
-)
+
 
 
 # Class for loading and parsing G-code files
@@ -29,7 +24,15 @@ class GCodeReader(MeshReader):
 
     def __init__(self) -> None:
         super().__init__()
+        MimeTypeDatabase.addMimeType(
+            MimeType(
+                name = "application/x-cura-gcode-file",
+                comment = "Cura GCode File",
+                suffixes = ["gcode"]
+            )
+        )
         self._supported_extensions = [".gcode", ".g"]
+
         self._flavor_reader = None
 
         Application.getInstance().getPreferences().addPreference("gcodereader/show_caution", True)
diff --git a/plugins/UFPWriter/UFPWriter.py b/plugins/UFPWriter/UFPWriter.py
index a85ee489cb..d318a0e77d 100644
--- a/plugins/UFPWriter/UFPWriter.py
+++ b/plugins/UFPWriter/UFPWriter.py
@@ -1,5 +1,6 @@
 #Copyright (c) 2018 Ultimaker B.V.
 #Cura is released under the terms of the LGPLv3 or higher.
+
 from typing import cast
 
 from Charon.VirtualFile import VirtualFile #To open UFP files.
@@ -9,6 +10,7 @@ from io import StringIO #For converting g-code to bytes.
 from UM.Application import Application
 from UM.Logger import Logger
 from UM.Mesh.MeshWriter import MeshWriter #The writer we need to implement.
+from UM.MimeTypeDatabase import MimeTypeDatabase, MimeType
 from UM.PluginRegistry import PluginRegistry #To get the g-code writer.
 from PyQt5.QtCore import QBuffer
 
@@ -22,6 +24,15 @@ catalog = i18nCatalog("cura")
 class UFPWriter(MeshWriter):
     def __init__(self):
         super().__init__(add_to_recent_files = False)
+
+        MimeTypeDatabase.addMimeType(
+            MimeType(
+                name = "application/x-cura-stl-file",
+                comment = "Cura UFP File",
+                suffixes = ["ufp"]
+            )
+        )
+
         self._snapshot = None
         Application.getInstance().getOutputDeviceManager().writeStarted.connect(self._createSnapshot)
 
diff --git a/plugins/UFPWriter/__init__.py b/plugins/UFPWriter/__init__.py
index a2ec99044f..9db6b042f8 100644
--- a/plugins/UFPWriter/__init__.py
+++ b/plugins/UFPWriter/__init__.py
@@ -11,16 +11,6 @@ except ImportError:
 
 from UM.i18n import i18nCatalog #To translate the file format description.
 from UM.Mesh.MeshWriter import MeshWriter #For the binary mode flag.
-from UM.MimeTypeDatabase import MimeTypeDatabase, MimeType
-
-
-MimeTypeDatabase.addMimeType(
-    MimeType(
-        name = "application/x-cura-stl-file",
-        comment = "Cura UFP File",
-        suffixes = ["ufp"]
-    )
-)
 
 i18n_catalog = i18nCatalog("cura")
 
diff --git a/resources/definitions/fdmprinter.def.json b/resources/definitions/fdmprinter.def.json
index 2ca15ab646..823635a62a 100644
--- a/resources/definitions/fdmprinter.def.json
+++ b/resources/definitions/fdmprinter.def.json
@@ -230,6 +230,7 @@
                     "label": "Number of Extruders that are enabled",
                     "description": "Number of extruder trains that are enabled; automatically set in software",
                     "value": "machine_extruder_count",
+                    "default_value": 1,
                     "minimum_value": "1",
                     "maximum_value": "16",
                     "type": "int",