--- a/browser/components/feeds/FeedWriter.js
+++ b/browser/components/feeds/FeedWriter.js
@@ -98,19 +98,16 @@ FeedWriter.prototype = {
   },
 
   _setContentText(id, text) {
     let element = this._document.getElementById(id);
     let textNode = text.createDocumentFragment(element);
     while (element.hasChildNodes())
       element.firstChild.remove();
     element.appendChild(textNode);
-    if (text.base) {
-      element.setAttributeNS(XML_NS, "base", text.base.spec);
-    }
   },
 
   /**
    * Safely sets the href attribute on an anchor tag, providing the URI
    * specified can be loaded according to rules.
    * @param   element
    *          The element to set a URI attribute on
    * @param   attribute
@@ -287,18 +284,16 @@ FeedWriter.prototype = {
       let entryContainer = this._document.createElementNS(HTML_NS, "div");
       entryContainer.className = "entry";
 
       // If the entry has a title, make it a link
       if (entry.title) {
         let a = this._document.createElementNS(HTML_NS, "a");
         let span = this._document.createElementNS(HTML_NS, "span");
         a.appendChild(span);
-        if (entry.title.base)
-          span.setAttributeNS(XML_NS, "base", entry.title.base.spec);
         span.appendChild(entry.title.createDocumentFragment(a));
 
         // Entries are not required to have links, so entry.link can be null.
         if (entry.link)
           this._safeSetURIAttribute(a, "href", entry.link.spec);
 
         let title = this._document.createElementNS(HTML_NS, "h3");
         title.appendChild(a);
@@ -313,20 +308,16 @@ FeedWriter.prototype = {
 
         entryContainer.appendChild(title);
       }
 
       let body = this._document.createElementNS(HTML_NS, "div");
       let summary = entry.summary || entry.content;
       let docFragment = null;
       if (summary) {
-        if (summary.base)
-          body.setAttributeNS(XML_NS, "base", summary.base.spec);
-        else
-          LOG("no base?");
         docFragment = summary.createDocumentFragment(body);
         if (docFragment)
           body.appendChild(docFragment);
 
         // If the entry doesn't have a title, append a # permalink
         // See http://scripting.com/rss.xml for an example
         if (!entry.title && entry.link) {
           let a = this._document.createElementNS(HTML_NS, "a");

--- a/dom/base/FragmentOrElement.cpp
+++ b/dom/base/FragmentOrElement.cpp
@@ -355,81 +355,25 @@ nsIContent::GetLang() const
 
 already_AddRefed<nsIURI>
 nsIContent::GetBaseURI(bool aTryUseXHRDocBaseURI) const
 {
   if (IsInAnonymousSubtree() && IsAnonymousContentInSVGUseSubtree()) {
     nsIContent* bindingParent = GetBindingParent();
     MOZ_ASSERT(bindingParent);
     SVGUseElement* useElement = static_cast<SVGUseElement*>(bindingParent);
-    // XXX Ignore xml:base as we are removing it.
     if (URLExtraData* data = useElement->GetContentURLData()) {
       return do_AddRef(data->BaseURI());
     }
   }
 
   nsIDocument* doc = OwnerDoc();
   // Start with document base
   nsCOMPtr<nsIURI> base = doc->GetBaseURI(aTryUseXHRDocBaseURI);
 
-  // Collect array of xml:base attribute values up the parent chain. This
-  // is slightly slower for the case when there are xml:base attributes, but
-  // faster for the far more common case of there not being any such
-  // attributes.
-  // Also check for SVG elements which require special handling
-  AutoTArray<nsString, 5> baseAttrs;
-  nsString attr;
-  const nsIContent *elem = this;
-  do {
-    // First check for SVG specialness (why is this SVG specific?)
-    if (elem->IsSVGElement()) {
-      nsIContent* bindingParent = elem->GetBindingParent();
-      if (bindingParent) {
-        nsXBLBinding* binding = bindingParent->GetXBLBinding();
-        if (binding) {
-          // XXX sXBL/XBL2 issue
-          // If this is an anonymous XBL element use the binding
-          // document for the base URI.
-          // XXX Will fail with xml:base
-          base = binding->PrototypeBinding()->DocURI();
-          break;
-        }
-      }
-    }
-
-    // Otherwise check for xml:base attribute
-    if (elem->IsElement()) {
-      elem->AsElement()->GetAttr(kNameSpaceID_XML, nsGkAtoms::base, attr);
-      if (!attr.IsEmpty()) {
-        baseAttrs.AppendElement(attr);
-      }
-    }
-    elem = elem->GetParent();
-  } while(elem);
-
-  if (!baseAttrs.IsEmpty()) {
-    doc->WarnOnceAbout(nsIDocument::eXMLBaseAttribute);
-    // Now resolve against all xml:base attrs
-    for (uint32_t i = baseAttrs.Length() - 1; i != uint32_t(-1); --i) {
-      nsCOMPtr<nsIURI> newBase;
-      nsresult rv = NS_NewURI(getter_AddRefs(newBase), baseAttrs[i],
-                              doc->GetDocumentCharacterSet(), base);
-      // Do a security check, almost the same as nsDocument::SetBaseURL()
-      // Only need to do this on the final uri
-      if (NS_SUCCEEDED(rv) && i == 0) {
-        rv = nsContentUtils::GetSecurityManager()->
-          CheckLoadURIWithPrincipal(NodePrincipal(), newBase,
-                                    nsIScriptSecurityManager::STANDARD);
-      }
-      if (NS_SUCCEEDED(rv)) {
-        base.swap(newBase);
-      }
-    }
-  }
-
   return base.forget();
 }
 
 nsIURI*
 nsIContent::GetBaseURIForStyleAttr() const
 {
   if (IsInAnonymousSubtree() && IsAnonymousContentInSVGUseSubtree()) {
     nsIContent* bindingParent = GetBindingParent();

--- a/dom/base/nsDeprecatedOperationList.h
+++ b/dom/base/nsDeprecatedOperationList.h
@@ -34,10 +34,9 @@ DEPRECATED_OPERATION(RTCPeerConnectionGe
 DEPRECATED_OPERATION(AppCache)
 DEPRECATED_OPERATION(AppCacheInsecure)
 DEPRECATED_OPERATION(PrefixedImageSmoothingEnabled)
 DEPRECATED_OPERATION(PrefixedFullscreenAPI)
 DEPRECATED_OPERATION(LenientSetter)
 DEPRECATED_OPERATION(FileLastModifiedDate)
 DEPRECATED_OPERATION(ImageBitmapRenderingContext_TransferImageBitmap)
 DEPRECATED_OPERATION(URLCreateObjectURL_MediaStream)
-DEPRECATED_OPERATION(XMLBaseAttribute)
 DEPRECATED_OPERATION(WindowContentUntrusted)

--- a/dom/base/test/test_base.xhtml
+++ b/dom/base/test/test_base.xhtml
@@ -16,34 +16,34 @@
 SimpleTest.waitForExplicitFinish();
 addLoadEvent(function() {
   is(document.baseURI, "http://mochi.test:8888/tests/dom/base/",
      "document base");
   is(document.body.baseURI, "http://mochi.test:8888/tests/dom/base/",
      "body base");
 
   var expected =
-    ["http://mochi.test:8888/tests/dom/base/supercalifragilisticexpialidocious",
-     "http://mochi.test:8888/tests/dom/base/supercalifragilisticexpialidocious",
-     "http://mochi.test:8888/tests/dom/base/hello/",
-     "http://mochi.test:8888/tests/dom/base/hello/world",
-     "http://mochi.test:8888/tests/dom/base/hello/world#iamtheverymodelofamodernmajorgeneral",
-     "http://mochi.test:8888/tests/dom/base/hello/world#iamtheverymodelofamodernmajorgeneral",
+    ["http://mochi.test:8888/tests/dom/base/",
+     "http://mochi.test:8888/tests/dom/base/",
+     "http://mochi.test:8888/tests/dom/base/",
+     "http://mochi.test:8888/tests/dom/base/",
+     "http://mochi.test:8888/tests/dom/base/",
+     "http://mochi.test:8888/tests/dom/base/",
      ];
   var node = document.getElementById("1");
   while(node) {
     is(node.baseURI, expected.shift(), "node base");
     node = node.firstChild;
   }
   is(expected.length, 0, "found all expected nodes");
 
   var svgExpected =
-    ["http://mochi.test:8888/tests/dom/base/test/file_base_xbl.xml",
-     "http://mochi.test:8888/tests/dom/base/test/file_base_xbl.xml",
-     "http://mochi.test:8888/tests/dom/base/test/file_base_xbl.xml#shesellsseashellsbytheseashore",
+    ["http://mochi.test:8888/tests/dom/base/",
+     "http://mochi.test:8888/tests/dom/base/",
+     "http://mochi.test:8888/tests/dom/base/",
      ];
   node = SpecialPowers.wrap(document).getAnonymousNodes(document.getElementById("bound"))[0];
   while(node) {
     is(node.baseURI, svgExpected.shift(), "node base");
     node = node.firstChild;
   }
   is(svgExpected.length, 0, "found all expected nodes");
 

--- a/dom/html/test/test_bug481335.xhtml
+++ b/dom/html/test/test_bug481335.xhtml
@@ -58,21 +58,22 @@ function checkLinkColor(aElmId, aExpecte
     setTimeout(continueTest, 0);
     return false;
   }
   is(getColor(), aExpectedColor, aMessage);
   return true;
 }
 
 function* testIterator() {
+  let path = "http://mochi.test:8888/tests/dom/html/test/";
   // After first load
   $("newparent").appendChild($("t"));
-  is($("t").href, "http://www.example.com/" + rand,
+  is($("t").href, path + rand,
      "Unexpected href after move");
-  is($("t").href, "http://www.example.com/" + rand,
+  is($("t").href, path + rand,
      "Unexpected cached href after move");
   while (!checkLinkColor("t", unvisitedColor, "Should be unvisited now"))
     yield undefined;
 
   $("i").src = $("t").href;
   yield undefined;
 
   // After second load

--- a/dom/locales/en-US/chrome/dom/dom.properties
+++ b/dom/locales/en-US/chrome/dom/dom.properties
@@ -322,18 +322,16 @@ GeolocationInsecureRequestIsForbidden=A 
 # LOCALIZATION NOTE: Do not translate "Large-Allocation", as it is a literal header name.
 LargeAllocationNonWin32=This page would be loaded in a new process due to a Large-Allocation header, however Large-Allocation process creation is disabled on non-Win32 platforms.
 # LOCALIZATION NOTE: Do not translate URL.createObjectURL(MediaStream).
 URLCreateObjectURL_MediaStreamWarning=URL.createObjectURL(MediaStream) is deprecated and will be removed soon.
 # LOCALIZATION NOTE: Do not translate MozAutoGainControl or autoGainControl.
 MozAutoGainControlWarning=mozAutoGainControl is deprecated. Use autoGainControl instead.
 # LOCALIZATION NOTE: Do not translate mozNoiseSuppression or noiseSuppression.
 MozNoiseSuppressionWarning=mozNoiseSuppression is deprecated. Use noiseSuppression instead.
-# LOCALIZATION NOTE: Do not translate xml:base.
-XMLBaseAttributeWarning=Use of xml:base attribute is deprecated and will be removed soon. Please remove any use of it.
 # LOCALIZATION NOTE: Do not translate "content", "Window", and "window.top"
 WindowContentUntrustedWarning=The ‘content’ attribute of Window objects is deprecated.  Please use ‘window.top’ instead.
 # LOCALIZATION NOTE: The first %S is the tag name of the element that starts the loop, the second %S is the element's ID.
 SVGRefLoopWarning=The SVG <%S> with ID “%S” has a reference loop.
 # LOCALIZATION NOTE: The first %S is the tag name of the element in the chain where the chain was broken, the second %S is the element's ID.
 SVGRefChainLengthExceededWarning=An SVG <%S> reference chain which is too long was abandoned at the element with ID “%S”.
 # LOCALIZATION NOTE: Do not translate "<script>".
 ScriptSourceEmpty=‘%S’ attribute of <script> element is empty.

--- a/dom/xhr/tests/test_XHRDocURI.html
+++ b/dom/xhr/tests/test_XHRDocURI.html
@@ -33,31 +33,25 @@ function startTest() {
     gen = runTest();
     gen.next();
   });
 }
 
 function testXMLDocURI(aDoc, aExpects) {
   is(aDoc.documentURI, aExpects.documentURI, "wrong url");
   is(aDoc.baseURI, aExpects.baseURI, "wrong base");
-  is(aDoc.documentElement.baseURI, aExpects.elementBaseURI,
-     "wrong base (xml:base)");
 }
 
 function testChromeXMLDocURI(aDoc, aExpects) {
   is(aDoc.documentURI, aExpects.documentURI, "wrong url");
   is(aDoc.documentURIObject.spec, aExpects.documentURI,
      "wrong url (.documentObjectURI)");
   is(aDoc.baseURI, aExpects.baseURI, "wrong base");
   is(aDoc.baseURIObject.spec, aExpects.baseURI,
      "wrong base (.baseURIObject)");
-  is(aDoc.documentElement.baseURI, aExpects.elementBaseURI,
-     "wrong base (xml:base)");
-  is(aDoc.documentElement.baseURIObject.spec, aExpects.elementBaseURI,
-     "wrong base (.baseURIObject, xml:base)");
 }
 
 function testHTMLDocURI(aDoc, aExpects) {
   is(aDoc.documentURI, aExpects.documentURI, "wrong url");
   is(aDoc.baseURI, aExpects.baseURI, "wrong base");
 
   var base = aDoc.createElement("base");
   var newBaseURI = "http://www.example.com/";
@@ -69,28 +63,16 @@ function testHTMLDocURI(aDoc, aExpects) 
 function testChromeHTMLDocURI(aDoc, aNonChromeBaseURI, aExpects) {
   is(aDoc.documentURI, aExpects.documentURI, "wrong url");
   is(aDoc.documentURIObject.spec, aExpects.documentURI,
      "wrong url (.documentURIObject)");
   is(aDoc.baseURI, aExpects.baseURI, "wrong base");
   is(aDoc.baseURIObject.spec, aExpects.baseURI,
      "wrong url (.baseURIObject)");
 
-  aDoc.body.setAttributeNS("http://www.w3.org/XML/1998/namespace", "base",
-                           aNonChromeBaseURI);
-  is(aDoc.body.baseURI, aNonChromeBaseURI,
-     "wrong base (doc base and xml:base are same)");
-  is(aDoc.body.baseURIObject.spec, aNonChromeBaseURI,
-     "wrong base (.baseURIObject, doc base and xml:base are same)")
-  var attr = aDoc.getElementById("data").getAttributeNode("id");
-  is(attr.baseURI, aNonChromeBaseURI,
-     "wrong attr base (doc base and xml:base are same)")
-  is(attr.baseURIObject.spec, aNonChromeBaseURI,
-     "wrong attr base (.baseURIObject, doc base and xml:base are same)")
-
   var base = aDoc.createElement("base");
   var newBaseURI = "http://www.example.com/";
   base.href = newBaseURI;
   aDoc.head.appendChild(base);
   is(aDoc.baseURI, newBaseURI, "wrong base (after <base> changed)");
   is(aDoc.baseURIObject.spec, newBaseURI,
      "wrong base (.baseURIObject, after <base> changed)");
 }