contextSearcher.uc.js causes IME disabled in e10s

[fhoshino]

When e10s is enabled, right click from textarea and use contextSearcher.uc.js, after new tab poped up, IME is disabled on parent page, especially easy to trigger on Telegram Web and WhatsApp Web.

[fhoshino]

Same behaviour as this bug:
https://bugzilla.mozilla.org/show_bug.cgi?id=1266815