diff --git a/ports/cef/command_line.rs b/ports/cef/command_line.rs
index 9af3709f4cd..7f70c77bafa 100644
--- a/ports/cef/command_line.rs
+++ b/ports/cef/command_line.rs
@@ -32,12 +32,11 @@ fn command_line_new() -> *mut command_line_t {
 
 pub fn command_line_init(argc: c_int, argv: *const *const u8) {
     unsafe {
-        let mut a: Vec<String> = vec!();
-        for i in 0..(argc as usize) {
-            let slice = ffi::CStr::from_ptr(*argv.offset(i as isize) as *const c_char);
-            let s = str::from_utf8(slice.to_bytes()).unwrap();
-            a.push(s.to_owned());
-        }
+        let args = slice::from_raw_parts(argv, argc as usize);
+        let a = args.iter().map(|&arg| {
+            let slice = ffi::CStr::from_ptr(arg as *const c_char);
+            str::from_utf8(slice.to_bytes()).unwrap().to_owned()
+        }).collect();
         let cl = command_line_new();
         (*cl).argc = argc;
         (*cl).argv = a;
diff --git a/ports/cef/string.rs b/ports/cef/string.rs
index 523c4f66d2d..6e5324d3f7c 100644
--- a/ports/cef/string.rs
+++ b/ports/cef/string.rs
@@ -71,7 +71,7 @@ pub extern "C" fn cef_string_utf8_clear(cs: *mut cef_string_utf8_t) {
         (*cs).dtor.map(|dtor| dtor((*cs).str));
         (*cs).length = 0;
         (*cs).str = 0 as *mut u8;
-        (*cs).dtor = mem::transmute(0 as *const u8);
+        (*cs).dtor = None;
     }
 }
 
@@ -89,19 +89,19 @@ pub extern "C" fn cef_string_utf8_set(src: *const u8, src_len: size_t, output: *
     unsafe {
        if copy != 0 {
            if !src.is_null() && src_len > 0 {
-             (*output).str = libc::calloc(1, src_len + 1) as *mut u8;
-             if (*output).str.is_null() {
-                 return 0;
-             }
+               (*output).str = libc::calloc(1, src_len + 1) as *mut u8;
+               if (*output).str.is_null() {
+                   return 0;
+               }
 
-             ptr::copy(src, (*output).str, src_len as usize);
-             (*output).length = src_len;
-             (*output).dtor = Some(string_utf8_dtor as extern "C" fn(*mut u8));
+               ptr::copy(src, (*output).str, src_len as usize);
+               (*output).length = src_len;
+               (*output).dtor = Some(string_utf8_dtor as extern "C" fn(*mut u8));
            }
        } else {
-         (*output).str = mem::transmute(src);
-         (*output).length = src_len;
-         (*output).dtor = mem::transmute(0 as *const u8);
+           (*output).str = src as *mut _;
+           (*output).length = src_len;
+           (*output).dtor = None;
        }
     }
     return 1;
@@ -151,7 +151,7 @@ pub extern "C" fn cef_string_utf16_clear(cs: *mut cef_string_utf16_t) {
         (*cs).dtor.map(|dtor| dtor((*cs).str));
         (*cs).length = 0;
         (*cs).str = 0 as *mut c_ushort;
-        (*cs).dtor = mem::transmute(0 as *const u8);
+        (*cs).dtor = None;
     }
 }
 
@@ -169,20 +169,20 @@ pub extern "C" fn cef_string_utf16_set(src: *const c_ushort, src_len: size_t, ou
     unsafe {
        if copy != 0 {
            if !src.is_null() && src_len > 0 {
-             (*output).str = libc::calloc(1, (src_len + 1) * mem::size_of::<c_ushort>() as u64) as
-                 *mut u16;
-             if (*output).str.is_null() {
-                 return 0;
-             }
+               (*output).str = libc::calloc(1, (src_len + 1) * mem::size_of::<c_ushort>() as u64) as
+                   *mut u16;
+               if (*output).str.is_null() {
+                   return 0;
+               }
 
-             ptr::copy(src, (*output).str, src_len as usize);
-             (*output).length = src_len;
-             (*output).dtor = Some(string_utf16_dtor as extern "C" fn(*mut c_ushort));
+               ptr::copy(src, (*output).str, src_len as usize);
+               (*output).length = src_len;
+               (*output).dtor = Some(string_utf16_dtor as extern "C" fn(*mut c_ushort));
            }
        } else {
-         (*output).str = mem::transmute(src);
-         (*output).length = src_len;
-         (*output).dtor = mem::transmute(0 as *const u8);
+           (*output).str = src as *mut _;
+           (*output).length = src_len;
+           (*output).dtor = None;
        }
     }
     return 1;
@@ -209,7 +209,7 @@ pub extern "C" fn cef_string_wide_clear(cs: *mut cef_string_wide_t) {
         (*cs).dtor.map(|dtor| dtor((*cs).str));
         (*cs).length = 0;
         (*cs).str = 0 as *mut wchar_t;
-        (*cs).dtor = mem::transmute(0 as *const u8);
+        (*cs).dtor = None;
     }
 }
 
@@ -227,20 +227,20 @@ pub extern "C" fn cef_string_wide_set(src: *const wchar_t, src_len: size_t, outp
     unsafe {
        if copy != 0 {
            if !src.is_null() && src_len > 0 {
-             (*output).str = libc::calloc(1, (src_len + 1) * mem::size_of::<wchar_t>() as u64) as
-                 *mut wchar_t;
-             if (*output).str.is_null() {
-                 return 0;
-             }
+               (*output).str = libc::calloc(1, (src_len + 1) * mem::size_of::<wchar_t>() as u64) as
+                   *mut wchar_t;
+               if (*output).str.is_null() {
+                   return 0;
+               }
 
-             ptr::copy(src, (*output).str, src_len as usize);
-             (*output).length = src_len;
-             (*output).dtor = Some(string_wide_dtor as extern "C" fn(*mut wchar_t));
+               ptr::copy(src, (*output).str, src_len as usize);
+               (*output).length = src_len;
+               (*output).dtor = Some(string_wide_dtor as extern "C" fn(*mut wchar_t));
            }
        } else {
-         (*output).str = mem::transmute(src);
-         (*output).length = src_len;
-         (*output).dtor = mem::transmute(0 as *const u8);
+           (*output).str = src as *mut _;
+           (*output).length = src_len;
+           (*output).dtor = None;
        }
     }
     return 1;
@@ -311,8 +311,8 @@ pub fn empty_utf16_string() -> cef_string_utf16_t {
 
 pub fn string_to_userfree_string(string: cef_string_utf16_t) -> cef_string_userfree_utf16_t {
     unsafe {
-        let allocation: cef_string_userfree_utf16_t =
-            mem::transmute(libc::malloc(mem::size_of::<cef_string_utf16_t>() as size_t));
+        let allocation = libc::malloc(mem::size_of::<cef_string_utf16_t>() as size_t)
+            as cef_string_userfree_utf16_t;
         ptr::write(allocation, string);
         allocation
     }
diff --git a/ports/cef/string_list.rs b/ports/cef/string_list.rs
index a9a2dfc5252..26897552ea3 100644
--- a/ports/cef/string_list.rs
+++ b/ports/cef/string_list.rs
@@ -3,33 +3,25 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use libc::{c_int};
-use std::mem;
+use std::boxed;
 use std::slice;
 use string::cef_string_utf16_set;
 use types::{cef_string_list_t,cef_string_t};
 
 use rustc_unicode::str::Utf16Encoder;
 
-fn string_list_to_vec(lt: *mut cef_string_list_t) -> *mut Vec<String> {
-    lt as *mut Vec<String>
-}
-
 //cef_string_list
 
 #[no_mangle]
 pub extern "C" fn cef_string_list_alloc() -> *mut cef_string_list_t {
-    unsafe {
-         let lt: Box<Vec<String>> = box vec!();
-         mem::transmute(lt)
-    }
+    boxed::into_raw(box vec!())
 }
 
 #[no_mangle]
 pub extern "C" fn cef_string_list_size(lt: *mut cef_string_list_t) -> c_int {
     unsafe {
         if lt.is_null() { return 0; }
-        let v = string_list_to_vec(lt);
-        (*v).len() as c_int
+        (*lt).len() as c_int
     }
 }
 
@@ -37,8 +29,7 @@ pub extern "C" fn cef_string_list_size(lt: *mut cef_string_list_t) -> c_int {
 pub extern "C" fn cef_string_list_append(lt: *mut cef_string_list_t, value: *const cef_string_t) {
     unsafe {
         if lt.is_null() { return; }
-        let v = string_list_to_vec(lt);
-        (*v).push(String::from_utf16(slice::from_raw_parts((*value).str, (*value).length as usize)).unwrap());
+        (*lt).push(String::from_utf16(slice::from_raw_parts((*value).str, (*value).length as usize)).unwrap());
     }
 }
 
@@ -46,11 +37,10 @@ pub extern "C" fn cef_string_list_append(lt: *mut cef_string_list_t, value: *con
 pub extern "C" fn cef_string_list_value(lt: *mut cef_string_list_t, index: c_int, value: *mut cef_string_t) -> c_int {
     unsafe {
         if index < 0 || lt.is_null() { return 0; }
-        let v = string_list_to_vec(lt);
-        if index as usize > (*v).len() - 1 { return 0; }
-        let ref string = (*v)[index as usize];
+        if index as usize > (*lt).len() - 1 { return 0; }
+        let ref string = (*lt)[index as usize];
         let utf16_chars: Vec<u16> = Utf16Encoder::new(string.chars()).collect();
-        cef_string_utf16_set(mem::transmute(utf16_chars.as_ptr()), utf16_chars.len() as u64, value, 1)
+        cef_string_utf16_set(utf16_chars.as_ptr(), utf16_chars.len() as u64, value, 1)
     }
 }
 
@@ -58,8 +48,7 @@ pub extern "C" fn cef_string_list_value(lt: *mut cef_string_list_t, index: c_int
 pub extern "C" fn cef_string_list_clear(lt: *mut cef_string_list_t) {
     unsafe {
         if lt.is_null() { return; }
-        let v = string_list_to_vec(lt);
-        (*v).clear();
+        (*lt).clear();
     }
 }
 
@@ -67,9 +56,8 @@ pub extern "C" fn cef_string_list_clear(lt: *mut cef_string_list_t) {
 pub extern "C" fn cef_string_list_free(lt: *mut cef_string_list_t) {
     unsafe {
         if lt.is_null() { return; }
-        let v: Box<Vec<String>> = mem::transmute(lt);
         cef_string_list_clear(lt);
-        drop(v);
+        drop(Box::from_raw(lt));
     }
 }
 
@@ -77,8 +65,7 @@ pub extern "C" fn cef_string_list_free(lt: *mut cef_string_list_t) {
 pub extern "C" fn cef_string_list_copy(lt: *mut cef_string_list_t) -> *mut cef_string_list_t {
     unsafe {
         if lt.is_null() { return 0 as *mut cef_string_list_t; }
-        let v = string_list_to_vec(lt);
-        let copy = (*v).clone();
-        mem::transmute(box copy)
+        let copy = (*lt).clone();
+        boxed::into_raw(box copy)
     }
 }
diff --git a/ports/cef/string_map.rs b/ports/cef/string_map.rs
index b7fd8dffcc3..3275fa910c0 100644
--- a/ports/cef/string_map.rs
+++ b/ports/cef/string_map.rs
@@ -4,33 +4,24 @@
 
 use eutil::slice_to_str;
 use libc::{c_int};
+use std::boxed;
 use std::collections::BTreeMap;
-use std::mem;
-use std::string::String;
 use string::{cef_string_userfree_utf16_alloc, cef_string_userfree_utf16_free};
 use string::{cef_string_utf16_set};
 use types::{cef_string_map_t, cef_string_t};
 
-fn string_map_to_treemap(sm: *mut cef_string_map_t) -> *mut BTreeMap<String, *mut cef_string_t> {
-    sm as *mut BTreeMap<String, *mut cef_string_t>
-}
-
 //cef_string_map
 
 #[no_mangle]
 pub extern "C" fn cef_string_map_alloc() -> *mut cef_string_map_t {
-    unsafe {
-         let sm: Box<BTreeMap<String, *mut cef_string_t>> = box BTreeMap::new();
-         mem::transmute(sm)
-    }
+    boxed::into_raw(box BTreeMap::new())
 }
 
 #[no_mangle]
 pub extern "C" fn cef_string_map_size(sm: *mut cef_string_map_t) -> c_int {
     unsafe {
         if sm.is_null() { return 0; }
-        let v = string_map_to_treemap(sm);
-        (*v).len() as c_int
+        (*sm).len() as c_int
     }
 }
 
@@ -38,11 +29,10 @@ pub extern "C" fn cef_string_map_size(sm: *mut cef_string_map_t) -> c_int {
 pub extern "C" fn cef_string_map_append(sm: *mut cef_string_map_t, key: *const cef_string_t, value: *const cef_string_t) -> c_int {
     unsafe {
         if sm.is_null() { return 0; }
-        let v = string_map_to_treemap(sm);
         slice_to_str((*key).str as *const u8, (*key).length as usize, |result| {
             let csv = cef_string_userfree_utf16_alloc();
             cef_string_utf16_set((*value).str as *const u16, (*value).length, csv, 1);
-            (*v).insert(result.to_owned(), csv);
+            (*sm).insert(result.to_owned(), csv);
             1
         })
     }
@@ -52,12 +42,10 @@ pub extern "C" fn cef_string_map_append(sm: *mut cef_string_map_t, key: *const c
 pub extern "C" fn cef_string_map_find(sm: *mut cef_string_map_t, key: *const cef_string_t, value: *mut cef_string_t) -> c_int {
     unsafe {
         if sm.is_null() { return 0; }
-        let v = string_map_to_treemap(sm);
         slice_to_str((*key).str as *const u8, (*key).length as usize, |result| {
-            match (*v).get(result) {
+            match (*sm).get(result) {
                 Some(s) => {
-                    cef_string_utf16_set((**s).str as *const u16, (**s).length, value, 1);
-                    1
+                    cef_string_utf16_set((**s).str as *const u16, (**s).length, value, 1)
                 }
                 None => 0
             }
@@ -69,48 +57,44 @@ pub extern "C" fn cef_string_map_find(sm: *mut cef_string_map_t, key: *const cef
 pub extern "C" fn cef_string_map_key(sm: *mut cef_string_map_t, index: c_int, value: *mut cef_string_t) -> c_int {
     unsafe {
         if index < 0 || sm.is_null() { return 0; }
-        let v = string_map_to_treemap(sm);
-        if index as usize > (*v).len() - 1 { return 0; }
+        if index as usize > (*sm).len() - 1 { return 0; }
 
-        for (i, k) in (*v).keys().enumerate() {
-            if i == index as usize {
+        match (*sm).keys().nth(index as usize) {
+            Some(k) => {
                 cef_string_utf16_set(k.as_bytes().as_ptr() as *const u16,
                                      k.len() as u64,
                                      value,
-                                     1);
-                return 1;
-            }
+                                     1)
+            },
+            None => 0,
         }
     }
-    0
 }
 
 #[no_mangle]
 pub extern "C" fn cef_string_map_value(sm: *mut cef_string_map_t, index: c_int, value: *mut cef_string_t) -> c_int {
     unsafe {
         if index < 0 || sm.is_null() { return 0; }
-        let v = string_map_to_treemap(sm);
-        if index as usize > (*v).len() - 1 { return 0; }
+        if index as usize > (*sm).len() - 1 { return 0; }
 
-        for (i, val) in (*v).values().enumerate() {
-            if i == index as usize {
+        match (*sm).values().nth(index as usize) {
+            Some(val) => {
                 cef_string_utf16_set((**val).str as *const u16, (**val).length, value, 1);
-                return 1;
-            }
+                1
+            },
+            None => 0,
         }
     }
-    0
 }
 
 #[no_mangle]
 pub extern "C" fn cef_string_map_clear(sm: *mut cef_string_map_t) {
     unsafe {
         if sm.is_null() { return; }
-        let v = string_map_to_treemap(sm);
-        for val in (*v).values() {
+        for val in (*sm).values() {
             cef_string_userfree_utf16_free(*val);
         }
-        (*v).clear();
+        (*sm).clear();
     }
 }
 
@@ -118,7 +102,7 @@ pub extern "C" fn cef_string_map_clear(sm: *mut cef_string_map_t) {
 pub extern "C" fn cef_string_map_free(sm: *mut cef_string_map_t) {
     unsafe {
         if sm.is_null() { return; }
-        let _v: Box<BTreeMap<String, *mut cef_string_t>> = mem::transmute(sm);
         cef_string_map_clear(sm);
+        drop(Box::from_raw(sm));
     }
 }
diff --git a/ports/cef/types.rs b/ports/cef/types.rs
index 5378d67b405..be71083f1ed 100644
--- a/ports/cef/types.rs
+++ b/ports/cef/types.rs
@@ -15,7 +15,7 @@ pub use self::cef_rect as cef_rect_t;
 
 use std::collections::BTreeMap;
 
-pub enum cef_string_map_t {}
+pub type cef_string_map_t = BTreeMap<String, *mut cef_string_t>;
 pub type cef_string_multimap_t = BTreeMap<String, Vec<*mut cef_string_t>>;
 pub type cef_string_list_t = Vec<String>;
 pub enum cef_text_input_context_t {}
diff --git a/ports/cef/wrappers.rs b/ports/cef/wrappers.rs
index dcdc686d9e5..ce6873521aa 100644
--- a/ports/cef/wrappers.rs
+++ b/ports/cef/wrappers.rs
@@ -38,7 +38,7 @@ use std::boxed;
 use std::collections::HashMap;
 use std::mem;
 use std::ptr;
-use std::raw;
+use std::slice;
 
 pub trait CefWrap<CObject> {
     fn to_c(rust_object: Self) -> CObject;
@@ -209,10 +209,7 @@ impl<'a> CefWrap<*const cef_string_t> for &'a [u16] {
         }
     }
     unsafe fn to_rust(cef_string: *const cef_string_t) -> &'a [u16] {
-        mem::transmute(raw::Slice {
-            data: (*cef_string).str,
-            len: (*cef_string).length as usize,
-        })
+        slice::from_raw_parts((*cef_string).str, (*cef_string).length as usize)
     }
 }