You have it backwards. tabs.browsers wasnt *supposed* to be a function.

content/completion.js

@@ -785,7 +785,7 @@ function Completion() //{{{
             let items = [];
             // FIXME: liberator.has("tabs")
 
-            for (let [i, browser] in tabs.browsers())
+            for (let [i, browser] in tabs.browsers)
             {
                 i = i + 1;
                 let title = "";

content/tabs.js

@@ -657,7 +657,7 @@ function Tabs() //{{{
 
         get alternate() alternates[1],
 
-        get browsers() function ()
+        get browsers()
         {
             let browsers = getBrowser().browsers;
             for (let i = 0; i < browsers.length; i++)

content/ui.js

@@ -1324,6 +1324,7 @@ function ItemList(id) //{{{
         if (typeof a == "function")
             a = a();
 
+        XML.ignoreWhitespace = true;
         let row =
             <ul class="compitem">
                 <li class="favicon">{a ? <img src={a}/> : <></>}</li>