Fix Sinhala rendering in facebook

Adds a temporary fix to add custom css to facebook.com to fix an issue with zwj not rendering correctly in facebook. Facebook renders zwj inside a span. This causes languages like Sinhala to not render text correctly. This extension injects css to remove the span by setting display: contents on the spans. Check screenshots for an example. source: https://github.com/thilinag/fix-sinhala-facebook