diff --git a/4chan_x.js b/4chan_x.js
index bd07b76d3..7e5c70377 100644
--- a/4chan_x.js
+++ b/4chan_x.js
@@ -2121,7 +2121,8 @@
   imgExpand = {
     init: function() {
       g.callbacks.push(imgExpand.cb.node);
-      return imgExpand.dialog();
+      imgExpand.dialog();
+      return $.addStyle("body.fitheight img[md5] + img { max-height: " + d.body.clientHeight + "px }");
     },
     cb: {
       node: function(root) {
@@ -2416,10 +2417,7 @@
       }\
       body.fitwidth img[md5] + img {\
         max-width: 100%;\
-      }\
-      body.fitheight img[md5] + img {\
-        /* FIXME max height = height of thread. we want height of viewport */\
-        max-height: 100%;\
+        width: -moz-calc(100%); /* hack so only firefox sees this */\
       }\
 \
       iframe {\
diff --git a/script.coffee b/script.coffee
index e84ab5628..6f161cbd7 100644
--- a/script.coffee
+++ b/script.coffee
@@ -1637,6 +1637,8 @@ imgExpand =
   init: ->
     g.callbacks.push imgExpand.cb.node
     imgExpand.dialog()
+    #FIXME add a resize listener
+    $.addStyle "body.fitheight img[md5] + img { max-height: #{d.body.clientHeight}px }"
 
   cb:
     node: (root) ->
@@ -1887,10 +1889,7 @@ main =
       }
       body.fitwidth img[md5] + img {
         max-width: 100%;
-      }
-      body.fitheight img[md5] + img {
-        /* FIXME max height = height of thread. we want height of viewport */
-        max-height: 100%;
+        width: -moz-calc(100%); /* hack so only firefox sees this */
       }
 
       iframe {