diff --git a/docshell/test/unit/test_nsDefaultURIFixup_info.js b/docshell/test/unit/test_nsDefaultURIFixup_info.js
index 9e33ea484f..c606ac32ef 100644
--- a/docshell/test/unit/test_nsDefaultURIFixup_info.js
+++ b/docshell/test/unit/test_nsDefaultURIFixup_info.js
@@ -426,8 +426,6 @@ var testcases = [ {
     protocolChange: true,
   }, {
     input: "?'.com",
-    fixedURI: "http:///?%27.com",
-    alternateURI: "http://www..com/?%27.com",
     keywordLookup: true,
     protocolChange: true,
   }, {
@@ -436,14 +434,10 @@ var testcases = [ {
     protocolChange: true
   }, {
     input: "?mozilla",
-    fixedURI: "http:///?mozilla",
-    alternateURI: "http://www..com/?mozilla",
     keywordLookup: true,
     protocolChange: true,
   }, {
     input: "??mozilla",
-    fixedURI: "http:///??mozilla",
-    alternateURI: "http://www..com/??mozilla",
     keywordLookup: true,
     protocolChange: true,
   }, {
diff --git a/dom/html/test/test_bug558788-1.html b/dom/html/test/test_bug558788-1.html
index 94b7a5f00e..4db61ed738 100644
--- a/dom/html/test/test_bug558788-1.html
+++ b/dom/html/test/test_bug558788-1.html
@@ -154,13 +154,14 @@ function checkInputURL()
   sendString("ttp://mozilla.org");
   checkValidApplies(element);
 
-  for (var i=0; i<13; ++i) {
+  for (var i=0; i<10; ++i) {
     synthesizeKey("VK_BACK_SPACE", {});
     checkValidApplies(element);
   }
 
   synthesizeKey("VK_BACK_SPACE", {});
-  for (var i=0; i<4; ++i) {
+  // "http://" is now invalid
+  for (var i=0; i<7; ++i) {
     checkInvalidApplies(element);
     synthesizeKey("VK_BACK_SPACE", {});
   }
diff --git a/dom/url/tests/test_url.html b/dom/url/tests/test_url.html
index d07a752bb4..73e75667d8 100644
--- a/dom/url/tests/test_url.html
+++ b/dom/url/tests/test_url.html
@@ -398,6 +398,18 @@
     is(url.href, "scheme://tmp\\test");
   </script>
 
+  <script>
+    /** Test for Bug 1275746 **/
+    SimpleTest.doesThrow(() => { var url = new URL("http:"); }, "http: is not a valid URL");
+    SimpleTest.doesThrow(() => { var url = new URL("http:///"); }, "http: is not a valid URL");
+
+    var url = new URL("file:");
+    is(url.href, "file:///", "Parsing file: should work.");
+
+    url = new URL("file:///");
+    is(url.href, "file:///", "Parsing file:/// should work.");
+  </script>
+
   <script>
     var url = new URL("scheme:path/to/file?query#hash");
     is(url.href, "scheme:path/to/file?query#hash");
diff --git a/extensions/cookie/test/unit/test_bug526789.js b/extensions/cookie/test/unit/test_bug526789.js
index 0eac1d4929..624044577c 100644
--- a/extensions/cookie/test/unit/test_bug526789.js
+++ b/extensions/cookie/test/unit/test_bug526789.js
@@ -79,23 +79,11 @@ function run_test() {
 
   cm.removeAll();
 
-  // test that setting an empty or '.' http:// host results in a no-op
   var uri = NetUtil.newURI("http://baz.com/");
-  var emptyuri = NetUtil.newURI("http:///");
-  var doturi = NetUtil.newURI("http://./");
   do_check_eq(uri.asciiHost, "baz.com");
-  do_check_eq(emptyuri.asciiHost, "");
-  do_check_eq(doturi.asciiHost, ".");
-  cs.setCookieString(emptyuri, null, "foo2=bar", null);
-  do_check_eq(getCookieCount(), 0);
-  cs.setCookieString(doturi, null, "foo3=bar", null);
-  do_check_eq(getCookieCount(), 0);
   cs.setCookieString(uri, null, "foo=bar", null);
-  do_check_eq(getCookieCount(), 1);
 
   do_check_eq(cs.getCookieString(uri, null), "foo=bar");
-  do_check_eq(cs.getCookieString(emptyuri, null), null);
-  do_check_eq(cs.getCookieString(doturi, null), null);
 
   do_check_eq(cm.countCookiesFromHost(""), 0);
   do_check_throws(function() {
diff --git a/netwerk/base/nsStandardURL.cpp b/netwerk/base/nsStandardURL.cpp
index bc1350f28f..983e938caf 100644
--- a/netwerk/base/nsStandardURL.cpp
+++ b/netwerk/base/nsStandardURL.cpp
@@ -1483,6 +1483,11 @@ nsStandardURL::SetSpec(const nsACString &input)
         rv = BuildNormalizedSpec(spec);
     }
 
+    // Make sure that a URLTYPE_AUTHORITY has a non-empty hostname.
+    if (mURLType == URLTYPE_AUTHORITY && mHost.mLen == -1) {
+        rv = NS_ERROR_MALFORMED_URI;
+    }
+
     if (NS_FAILED(rv)) {
         Clear();
         // If parsing the spec has failed, restore the old URL
@@ -3092,20 +3097,26 @@ nsStandardURL::SetFile(nsIFile *file)
     rv = net_GetURLSpecFromFile(file, url);
     if (NS_FAILED(rv)) return rv;
 
-    SetSpec(url);
+    uint32_t oldURLType = mURLType;
+    uint32_t oldDefaultPort = mDefaultPort;
+    rv = Init(nsIStandardURL::URLTYPE_NO_AUTHORITY, -1, url, nullptr, nullptr);
 
-    rv = Init(mURLType, mDefaultPort, url, nullptr, nullptr);
+    if (NS_FAILED(rv)) {
+        // Restore the old url type and default port if the call to Init fails.
+        mURLType = oldURLType;
+        mDefaultPort = oldDefaultPort;
+        return rv;
+    }
 
     // must clone |file| since its value is not guaranteed to remain constant
-    if (NS_SUCCEEDED(rv)) {
-        InvalidateCache();
-        if (NS_FAILED(file->Clone(getter_AddRefs(mFile)))) {
-            NS_WARNING("nsIFile::Clone failed");
-            // failure to clone is not fatal (GetFile will generate mFile)
-            mFile = nullptr;
-        }
+    InvalidateCache();
+    if (NS_FAILED(file->Clone(getter_AddRefs(mFile)))) {
+        NS_WARNING("nsIFile::Clone failed");
+        // failure to clone is not fatal (GetFile will generate mFile)
+        mFile = nullptr;
     }
-    return rv;
+
+    return NS_OK;
 }
 
 //----------------------------------------------------------------------------
diff --git a/netwerk/test/unit/test_URIs.js b/netwerk/test/unit/test_URIs.js
index b68c4f7874..5bc7fe432d 100644
--- a/netwerk/test/unit/test_URIs.js
+++ b/netwerk/test/unit/test_URIs.js
@@ -92,18 +92,6 @@ var gTests = [
     ref:     "",
     relativeURI: "data/text/plain,2",
     nsIURL:  true, nsINestedURI: false },
-  { spec:    "ftp://",
-    scheme:  "ftp",
-    prePath: "ftp://",
-    path:    "/",
-    ref:     "",
-    nsIURL:  true, nsINestedURI: false },
-  { spec:    "ftp:///",
-    scheme:  "ftp",
-    prePath: "ftp://",
-    path:    "/",
-    ref:     "",
-    nsIURL:  true, nsINestedURI: false },
   { spec:    "ftp://ftp.mozilla.org/pub/mozilla.org/README",
     scheme:  "ftp",
     prePath: "ftp://ftp.mozilla.org",
@@ -135,18 +123,6 @@ var gTests = [
     path:    "//mozilla.org/",
     ref:     "",
     nsIURL:  false, nsINestedURI: false },
-  { spec:    "http://",
-    scheme:  "http",
-    prePath: "http://",
-    path:    "/",
-    ref:     "",
-    nsIURL:  true, nsINestedURI: false },
-  { spec:    "http:///",
-    scheme:  "http",
-    prePath: "http://",
-    path:    "/",
-    ref:     "",
-    nsIURL:  true, nsINestedURI: false },
   { spec:    "http://www.example.com/",
     scheme:  "http",
     prePath: "http://www.example.com",
diff --git a/netwerk/test/unit/test_standardurl.js b/netwerk/test/unit/test_standardurl.js
index 476c34b70b..c2b4dd3650 100644
--- a/netwerk/test/unit/test_standardurl.js
+++ b/netwerk/test/unit/test_standardurl.js
@@ -346,6 +346,14 @@ add_test(function test_backslashReplacement()
   run_next_test();
 });
 
+add_test(function test_authority_host()
+{
+  Assert.throws(() => { stringToURL("http:"); }, "TYPE_AUTHORITY should have host");
+  Assert.throws(() => { stringToURL("http:///"); }, "TYPE_AUTHORITY should have host");
+
+  run_next_test();
+});
+
 add_test(function test_trim_C0_and_space()
 {
   var url = stringToURL("\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f http://example.com/ \x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f ");
diff --git a/services/fxaccounts/tests/xpcshell/test_oauth_grant_client.js b/services/fxaccounts/tests/xpcshell/test_oauth_grant_client.js
index 244b79a5ee..710a65ee56 100644
--- a/services/fxaccounts/tests/xpcshell/test_oauth_grant_client.js
+++ b/services/fxaccounts/tests/xpcshell/test_oauth_grant_client.js
@@ -143,7 +143,7 @@ add_test(function serverErrorResponse () {
 
 add_test(function networkErrorResponse () {
   let client = new FxAccountsOAuthGrantClient({
-    serverURL: "http://",
+    serverURL: "http://domain.dummy",
     client_id: "abc123"
   });
   Services.prefs.setBoolPref("identity.fxaccounts.skipDeviceRegistration", true);
diff --git a/services/fxaccounts/tests/xpcshell/test_profile_client.js b/services/fxaccounts/tests/xpcshell/test_profile_client.js
index 2243da3aab..20ff6efc61 100644
--- a/services/fxaccounts/tests/xpcshell/test_profile_client.js
+++ b/services/fxaccounts/tests/xpcshell/test_profile_client.js
@@ -268,7 +268,7 @@ add_test(function server401ResponsePersists () {
 
 add_test(function networkErrorResponse () {
   let client = new FxAccountsProfileClient({
-    serverURL: "http://",
+    serverURL: "http://domain.dummy",
     fxa: mockFxa,
   });
   client.fetchProfile()
diff --git a/testing/web-platform/meta/XMLHttpRequest/open-url-bogus.htm.ini b/testing/web-platform/meta/XMLHttpRequest/open-url-bogus.htm.ini
deleted file mode 100644
index ef7b5d9100..0000000000
--- a/testing/web-platform/meta/XMLHttpRequest/open-url-bogus.htm.ini
+++ /dev/null
@@ -1,11 +0,0 @@
-[open-url-bogus.htm]
-  type: testharness
-  [XMLHttpRequest: open() - bogus URLs (http:)]
-    expected: FAIL
-
-  [XMLHttpRequest: open() - bogus URLs (ftp:)]
-    expected: FAIL
-
-  [XMLHttpRequest: open() - bogus URLs (http:////////////)]
-    expected: FAIL
-
diff --git a/testing/web-platform/meta/url/url-constructor.html.ini b/testing/web-platform/meta/url/url-constructor.html.ini
index 6da03043b2..22fddbc15e 100644
--- a/testing/web-platform/meta/url/url-constructor.html.ini
+++ b/testing/web-platform/meta/url/url-constructor.html.ini
@@ -219,6 +219,3 @@
   [Parsing: <http://example.com/foo/%2e./%2e%2e/.%2e/%2e.bar> against <about:blank>]
     expected: FAIL
 
-  [Parsing: <http:> against <https://example.org/foo/bar>]
-    expected: FAIL
-
diff --git a/toolkit/components/passwordmgr/test/unit/test_logins_search.js b/toolkit/components/passwordmgr/test/unit/test_logins_search.js
index 188c75039d..7307719812 100644
--- a/toolkit/components/passwordmgr/test/unit/test_logins_search.js
+++ b/toolkit/components/passwordmgr/test/unit/test_logins_search.js
@@ -192,7 +192,6 @@ add_task(function test_search_all_full_case_sensitive()
 {
   checkAllSearches({ hostname: "http://www.example.com" }, 1);
   checkAllSearches({ hostname: "http://www.example.com/" }, 0);
-  checkAllSearches({ hostname: "http://" }, 0);
   checkAllSearches({ hostname: "example.com" }, 0);
 
   checkAllSearches({ formSubmitURL: "http://www.example.com" }, 2);
diff --git a/toolkit/components/places/UnifiedComplete.js b/toolkit/components/places/UnifiedComplete.js
index ad3d35aab7..acd358b116 100644
--- a/toolkit/components/places/UnifiedComplete.js
+++ b/toolkit/components/places/UnifiedComplete.js
@@ -1245,7 +1245,7 @@ Search.prototype = {
     //  * If the protocol differs we should not match. For example if the user
     //    searched https we should not return http.
     try {
-      let prefixURI = NetUtil.newURI(this._strippedPrefix);
+      let prefixURI = NetUtil.newURI(this._strippedPrefix + match.token);
       let finalURI = NetUtil.newURI(match.url);
       if (prefixURI.scheme != finalURI.scheme)
         return false;
diff --git a/toolkit/components/places/nsNavHistory.cpp b/toolkit/components/places/nsNavHistory.cpp
index 8cf3a2e324..7f4007c1ab 100644
--- a/toolkit/components/places/nsNavHistory.cpp
+++ b/toolkit/components/places/nsNavHistory.cpp
@@ -949,6 +949,10 @@ nsresult // static
 nsNavHistory::AsciiHostNameFromHostString(const nsACString& aHostName,
                                           nsACString& aAscii)
 {
+  aAscii.Truncate();
+  if (aHostName.IsEmpty()) {
+    return NS_OK;
+  }
   // To properly generate a uri we must provide a protocol.
   nsAutoCString fakeURL("http://");
   fakeURL.Append(aHostName);