ochameau/addon-sdk — comment on commit c40523510f98b6ade2a4f2250540fdea258fbc6c
File: python-lib/cuddlefish/xpi.py line 108
By warner:

one caution about zf.writestr() is to check the file modes: unpack the .xpi (with unzip) and double-check that the file is world-readable. I found that writestr() doesn't always put a sensible mode into the .zip file, whereas zf.write() is more likely to copy the mode from the on-disk tempfile.