Fix harfbuzz issues by setting QT_HARFBUZZ=old

TODO

@@ -38,7 +38,6 @@ proper exception handling with saving pages
 Minor features/bugs
 ===================
 
-Mayhaps set QT_HARFBUZZ=old -- this doesn't seem to be possible the easy way (os.environ)
 progress bar is often red
 titles are still weird (and not attached to tab obj)
 Hiding scrollbars

qutebrowser/app.py

@@ -6,6 +6,12 @@ import faulthandler
 from signal import signal, SIGINT
 from argparse import ArgumentParser
 
+# This is a really old place to do this, but we have to do this before
+# importing PyQt or it won't work.
+# See https://bugreports.qt-project.org/browse/QTBUG-36099
+import qutebrowser.utils.harfbuzz as harfbuzz
+harfbuzz.fix()
+
 from PyQt5.QtWidgets import QApplication
 from PyQt5.QtCore import QUrl, QTimer
 

qutebrowser/utils/harfbuzz.py

@@ -0,0 +1,22 @@
+"""Fixer to set QT_HARFBUZZ variable.
+
+In its own file so it doesn't include any Qt stuff, because if it did, it
+wouldn't work.
+"""
+
+import os
+import sys
+
+
+def fix():
+    """Fix harfbuzz issues.
+
+    This switches to an older (but more stable) harfbuzz font rendering engine
+    instead of using the system wide one.
+
+    This fixes crashes on various sites.
+    See https://bugreports.qt-project.org/browse/QTBUG-36099
+    """
+    if sys.platform.startswith('linux'):
+        # Switch to old but stable font rendering engine
+        os.environ['QT_HARFBUZZ'] = 'old'