diff --git a/testing/mozharness/mozharness/mozilla/repo_manipulation.py b/testing/mozharness/mozharness/mozilla/repo_manipulation.py
index 52d3eba612c1..22b258ae56c9 100644
--- a/testing/mozharness/mozharness/mozilla/repo_manipulation.py
+++ b/testing/mozharness/mozharness/mozilla/repo_manipulation.py
@@ -1,4 +1,5 @@
 import ConfigParser
+import json
 import os
 
 from mozharness.base.errors import HgErrorList
@@ -138,6 +139,24 @@ class MercurialRepoManipulationMixin(object):
             error_list=HgErrorList
         )
 
+    def query_existing_tags(self, cwd, halt_on_failure=True):
+        cmd = self.query_exe('hg', return_type='list') + ['tags']
+        existing_tags = {}
+        output = self.get_output_from_command(
+            cmd, cwd=cwd, halt_on_failure=halt_on_failure
+        )
+        for line in output.splitlines():
+            parts = line.split(' ')
+            if len(parts) > 1:
+                # existing_tags = {TAG: REVISION, ...}
+                existing_tags[parts[0]] = parts[-1].split(':')[-1]
+        self.info(
+            "existing_tags:\n{}".format(
+                json.dumps(existing_tags, sort_keys=True, indent=4)
+            )
+        )
+        return existing_tags
+
     def push(self):
         """
             """
diff --git a/testing/mozharness/scripts/release/postrelease_version_bump.py b/testing/mozharness/scripts/release/postrelease_version_bump.py
index b06aca9f4187..ddc6542b9918 100644
--- a/testing/mozharness/scripts/release/postrelease_version_bump.py
+++ b/testing/mozharness/scripts/release/postrelease_version_bump.py
@@ -16,6 +16,7 @@ import sys
 
 sys.path.insert(1, os.path.dirname(os.path.dirname(sys.path[0])))
 from mozharness.base.vcs.vcsbase import MercurialScript
+from mozharness.base.vcs.mercurial import MercurialVCS
 from mozharness.mozilla.buildbot import BuildbotMixin
 from mozharness.mozilla.repo_manipulation import MercurialRepoManipulationMixin
 
@@ -152,8 +153,18 @@ class PostReleaseVersionBump(MercurialScript, BuildbotMixin,
         return ["-e", hg_ssh_opts, "-r", "."]
 
     def pull(self):
+        dirs = self.query_abs_dirs()
+        # bug 1417697 - clone default first, then pull to get the revision.
+        # This to deal with relbranches, which don't show up in mozilla-unified.
         super(PostReleaseVersionBump, self).pull(
                 repos=self.query_repos())
+        vcs_obj = MercurialVCS(log_obj=self.log_obj, config=self.config)
+        vcs_obj.pull(
+            self.config['repo']['repo'],
+            dirs['abs_gecko_dir'],
+            update_dest=False,
+            revision=self.config['revision']
+        )
 
     def bump_postrelease(self, *args, **kwargs):
         """Bump version"""
@@ -162,13 +173,38 @@ class PostReleaseVersionBump(MercurialScript, BuildbotMixin,
             curr_version = ".".join(self.get_version(dirs['abs_gecko_dir'], f["file"]))
             next_version = self.config['next_version']
 
-            if StrictVersion(next_version) <= StrictVersion(curr_version):
+            if StrictVersion(next_version) < StrictVersion(curr_version):
                 self.warning("Version bumping skipped due to conflicting values")
                 continue
+            elif StrictVersion(next_version) == StrictVersion(curr_version):
+                self.info("Version bumping skipped due to unchanged values")
+                continue
             else:
                 self.replace(os.path.join(dirs['abs_gecko_dir'], f["file"]),
                              curr_version, self.config["next_version"])
 
+    def check_tags(self, tag_names):
+        dirs = self.query_abs_dirs()
+        existing_tags = self.query_existing_tags(cwd=dirs['abs_gecko_dir'])
+        tags = []
+        for tag in tag_names:
+            if tag in existing_tags:
+                if self.config['revision'] == existing_tags[tag]:
+                    self.info(
+                        "Tag {} already exists on revision {}. Skipping...".format(
+                            tag, self.config['revision']
+                        )
+                    )
+                    continue
+                else:
+                    self.warning(
+                        "Tag {} exists on mismatched revision {}! Retagging...".format(
+                            tag, existing_tags[tag]
+                        )
+                    )
+            tags.append(tag)
+        return tags
+
     def tag(self):
         dirs = self.query_abs_dirs()
         tags = ["{product}_{version}_BUILD{build_number}",
@@ -177,6 +213,10 @@ class PostReleaseVersionBump(MercurialScript, BuildbotMixin,
                          version=self.config["version"].replace(".", "_"),
                          build_number=self.config["build_number"])
                 for t in tags]
+        tags = self.check_tags(tags)
+        if not tags:
+            self.info("No unique tags to add; skipping tagging.")
+            return
         message = "No bug - Tagging {revision} with {tags} a=release CLOSED TREE"
         message = message.format(
             revision=self.config["revision"],