diff --git a/builds/appchan-x.user.js b/builds/appchan-x.user.js
index c3ae74a1f..993900d21 100644
--- a/builds/appchan-x.user.js
+++ b/builds/appchan-x.user.js
@@ -10792,6 +10792,10 @@
       $.asap((function() {
         return post.file.fullImage[naturalHeight];
       }), function() {
+        if (isVideo) {
+          img.style.maxHeight = img[naturalHeight] + "px";
+          img.style.maxWidth = img['videoWidth'] + "px";
+        }
         return ImageExpand.completeExpand(post);
       });
       return $.after((img.controls ? thumb.parentNode : thumb), img);
diff --git a/builds/crx/script.js b/builds/crx/script.js
index 5f87c01b4..2ca5970a5 100644
--- a/builds/crx/script.js
+++ b/builds/crx/script.js
@@ -10830,6 +10830,10 @@
       $.asap((function() {
         return post.file.fullImage[naturalHeight];
       }), function() {
+        if (isVideo) {
+          img.style.maxHeight = img[naturalHeight] + "px";
+          img.style.maxWidth = img['videoWidth'] + "px";
+        }
         return ImageExpand.completeExpand(post);
       });
       return $.after((img.controls ? thumb.parentNode : thumb), img);
diff --git a/src/Images/ImageExpand.coffee b/src/Images/ImageExpand.coffee
index bcf21a8d8..f1eee2eb0 100644
--- a/src/Images/ImageExpand.coffee
+++ b/src/Images/ImageExpand.coffee
@@ -118,6 +118,10 @@ ImageExpand =
       img.controls = Conf['Show Controls']
     $.on img, 'error', ImageExpand.error
     $.asap (-> post.file.fullImage[naturalHeight]), ->
+      if isVideo
+        # XXX Firefox doesn't seem to size videos correctly?
+        img.style.maxHeight = img[naturalHeight] + "px"
+        img.style.maxWidth  = img['videoWidth']  + "px"
       ImageExpand.completeExpand post
     $.after (if img.controls then thumb.parentNode else thumb), img