--- a/mozharness/base/log.py
+++ b/mozharness/base/log.py
@@ -314,16 +314,17 @@ class BaseLogger(object):
         self.logger.addHandler(console_handler)
         self.all_handlers.append(console_handler)
 
     def add_file_handler(self, log_path, log_level=None, log_format=None,
                          date_format=None):
         if not self.append_to_log and os.path.exists(log_path):
             os.remove(log_path)
         file_handler = logging.FileHandler(log_path)
+        file_handler.setLevel(self.get_logger_level(log_level))
         file_handler.setFormatter(self.get_log_formatter(log_format=log_format,
                                                          date_format=date_format))
         self.logger.addHandler(file_handler)
         self.all_handlers.append(file_handler)
 
     def log_message(self, message, level=INFO, exit_code=-1, post_fatal_callback=None):
         """Generic log method.
         There should be more options here -- do or don't split by line,

--- a/mozharness/mozilla/building/buildbase.py
+++ b/mozharness/mozilla/building/buildbase.py
@@ -1323,17 +1323,21 @@ or run without that action (ie: --no-{ac
             '.zip',
         )
 
         # Some trees may not be setting uploadFiles, so default to []. Normally
         # we'd only expect to get here if the build completes successfully,
         # which means we should have uploadFiles.
         files = self.query_buildbot_property('uploadFiles') or []
         if not files:
-            self.warning('No files to upload to S3: uploadFiles property is missing or empty.')
+            self.warning('No files from the build system to upload to S3: uploadFiles property is missing or empty.')
+
+        # Also upload our mozharness log files
+        files.extend([os.path.join(self.log_obj.abs_log_dir, x) for x in self.log_obj.log_files.values()])
+
         for upload_file in files:
             # Create an S3 artifact for each file that gets uploaded. We also
             # check the uploaded file against the property conditions so that we
             # can set the buildbot config with the correct URLs for package
             # locations.
             tc.create_artifact(task, upload_file)
             if upload_file.endswith(valid_extensions):
                 for prop, condition in property_conditions:

--- a/mozharness/mozilla/taskcluster_helper.py
+++ b/mozharness/mozilla/taskcluster_helper.py
@@ -70,16 +70,17 @@ class Taskcluster(LogMixin):
                 "workerId": self.buildbot,
             })
 
     def create_artifact(self, task, filename):
         mime_types = {
             ".asc": "text/plain",
             ".checksums": "text/plain",
             ".json": "application/json",
+            ".log": "text/plain",
             ".tar.bz2": "application/x-gtar",
             ".txt": "text/plain",
             ".xpi": "application/x-xpinstall",
             ".zip": "application/zip",
         }
         mime_type = mime_types.get(os.path.splitext(filename)[1], 'application/octet-stream')
         content_length = os.path.getsize(filename)