--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3239,16 +3239,17 @@ source = "registry+https://github.com/ru
 
 [[package]]
 name = "xpcom"
 version = "0.1.0"
 dependencies = [
  "libc 0.2.43 (registry+https://github.com/rust-lang/crates.io-index)",
  "nserror 0.1.0",
  "nsstring 0.1.0",
+ "thin-vec 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "threadbound 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "xpcom_macros 0.1.0",
 ]
 
 [[package]]
 name = "xpcom-gtest"
 version = "0.1.0"
 dependencies = [

--- a/xpcom/idl-parser/xpidl/xpidl.py
+++ b/xpcom/idl-parser/xpidl/xpidl.py
@@ -418,20 +418,19 @@ class Typedef(object):
     def isScriptable(self):
         return self.realtype.isScriptable()
 
     def nativeType(self, calltype):
         return "%s %s" % (self.name, '*' if 'out' in calltype else '')
 
     def rustType(self, calltype):
         if self.name == 'nsresult':
-            return "%s::nserror::nsresult" % (calltype != 'in' and '*mut ' or '')
+            return "%s::nserror::nsresult" % ('*mut ' if 'out' in calltype else '')
 
-        return "%s%s" % (calltype != 'in' and '*mut ' or '',
-                         self.name)
+        return "%s%s" % ('*mut ' if 'out' in calltype else '', self.name)
 
     def __str__(self):
         return "typedef %s %s\n" % (self.type, self.name)
 
 
 class Forward(object):
     kind = 'forward'
 
@@ -463,16 +462,18 @@ class Forward(object):
     def nativeType(self, calltype):
         if calltype == 'element':
             return 'RefPtr<%s>' % self.name
         return "%s *%s" % (self.name, '*' if 'out' in calltype else '')
 
     def rustType(self, calltype):
         if rustBlacklistedForward(self.name):
             raise RustNoncompat("forward declaration %s is unsupported" % self.name)
+        if calltype == 'element':
+            return 'RefPtr<%s>' % self.name
         return "%s*const %s" % (calltype != 'in' and '*mut ' or '',
                                 self.name)
 
     def __str__(self):
         return "forward-declared %s\n" % self.name
 
 
 class Native(object):
@@ -594,16 +595,21 @@ class Native(object):
         if self.modifier not in ['ptr', 'ref']:
             raise RustNoncompat('Rust only supports [ref] / [ptr] native types')
 
         prefix = '*mut ' if 'out' in calltype else '*const '
         if 'out' in calltype and self.modifier == 'ptr':
             prefix += '*mut '
 
         if self.specialtype == 'nsid':
+            if 'element' in calltype:
+                if self.isPtr(calltype):
+                    raise IDLError("Array<nsIDPtr> not yet supported. "
+                                   "File an XPConnect bug if you need it.", self.location)
+                return self.nativename
             return prefix + self.nativename
         if self.specialtype in ['cstring', 'utf8string']:
             if 'element' in calltype:
                 return '::nsstring::nsCString'
             return prefix + '::nsstring::nsACString'
         if self.specialtype == 'astring':
             if 'element' in calltype:
                 return '::nsstring::nsString'
@@ -757,16 +763,18 @@ class Interface(object):
 
     def nativeType(self, calltype, const=False):
         if calltype == 'element':
             return 'RefPtr<%s>' % self.name
         return "%s%s *%s" % ('const ' if const else '', self.name,
                              '*' if 'out' in calltype else '')
 
     def rustType(self, calltype, const=False):
+        if calltype == 'element':
+            return 'RefPtr<%s>' % self.name
         return "%s*const %s" % ('*mut ' if 'out' in calltype else '',
                                 self.name)
 
     def __str__(self):
         l = ["interface %s\n" % self.name]
         if self.base is not None:
             l.append("\tbase %s\n" % self.base)
         l.append(str(self.attributes))
@@ -1326,19 +1334,26 @@ class Array(object):
         if 'out' in calltype:
             return '%s& ' % base
         elif 'in' == calltype:
             return 'const %s& ' % base
         else:
             return base
 
     def rustType(self, calltype):
-        # NOTE: To add Rust support, ensure 'element' is handled correctly in
-        # all rustType callees.
-        raise RustNoncompat("Array<...> types")
+        if calltype == 'legacyelement':
+            raise IDLError("[array] Array<T> is unsupported", self.location)
+
+        base = 'thin_vec::ThinVec<%s>' % self.type.rustType('element')
+        if 'out' in calltype:
+            return '*mut %s' % base
+        elif 'in' == calltype:
+            return '*const %s' % base
+        else:
+            return base
 
 
 TypeId = namedtuple('TypeId', 'name params')
 
 
 # Make str(TypeId) produce a nicer value
 TypeId.__str__ = lambda self: \
     "%s<%s>" % (self.name, ', '.join(str(p) for p in self.params)) \

--- a/xpcom/rust/xpcom/Cargo.toml
+++ b/xpcom/rust/xpcom/Cargo.toml
@@ -4,8 +4,9 @@ version = "0.1.0"
 authors = ["michael@thelayzells.com"]
 
 [dependencies]
 libc = "0.2"
 nsstring = { path = "../nsstring" }
 nserror = { path = "../nserror" }
 threadbound = "0.1"
 xpcom_macros = { path = "xpcom_macros" }
+thin-vec = { version = "0.1.0", features = ["gecko-ffi"] }

--- a/xpcom/rust/xpcom/src/lib.rs
+++ b/xpcom/rust/xpcom/src/lib.rs
@@ -10,16 +10,17 @@
 
 #![allow(non_snake_case)]
 #![allow(non_camel_case_types)]
 
 extern crate libc;
 extern crate nsstring;
 extern crate nserror;
 extern crate threadbound;
+extern crate thin_vec;
 
 // re-export the xpcom_macros macro
 #[macro_use]
 #[allow(unused_imports)]
 extern crate xpcom_macros;
 #[doc(hidden)]
 pub use xpcom_macros::*;