Add some FIXME comments about using ptr::NonNull

components/hashglobe/src/shim.rs

@@ -1,5 +1,6 @@
 use std::marker::PhantomData;
 
+// FIXME: remove this and use std::ptr::NonNull when Firefox requires Rust 1.25+
 pub struct NonZeroPtr<T: 'static>(&'static T);
 
 impl<T: 'static> NonZeroPtr<T> {

components/servo_arc/lib.rs

@@ -83,6 +83,7 @@ const MAX_REFCOUNT: usize = (isize::MAX) as usize;
 /// that this is all a temporary hack, this restriction is fine for now.
 ///
 /// [1]: https://github.com/rust-lang/rust/issues/27730
+// FIXME: remove this and use std::ptr::NonNull when Firefox requires Rust 1.25+
 pub struct NonZeroPtrMut<T: ?Sized + 'static>(&'static mut T);
 impl<T: ?Sized> NonZeroPtrMut<T> {
     pub fn new(ptr: *mut T) -> Self {

components/style/rule_tree/mod.rs

@@ -828,6 +828,8 @@ impl MallocSizeOf for RuleNode {
     }
 }
 
+// FIXME: use std::ptr::NonNull when Firefox requires Rust 1.25+
+
 #[derive(Clone)]
 struct WeakRuleNode {
     p: NonZeroPtrMut<RuleNode>,