fix(wx): Origin mismatch under Chromium
fix(wx): Origin mismatch under Chromium

Turns out workaround introduced for Firefox in #227
broke right-click "Upload to IPFS" function under Chromium ;-)

This commit adds userAgent check and enables workaround only
under Firefox, making Chromium (#218) happy.

lidel/ipfs-firefox-addon,lidel/ipfs-firefox-addon,lidel/ipfs-firefox-addon