Firefox 49 has added the support for 4-digit (
#RGBA) and 8-digit (
#RRGGBBAA) hexadecimal notations for RGBa colour values. Due to this change, previously invalid values could be valid, yielding unexpected results. A typical example is
#0000, which is now parsed as
transparent. You may want to double check your stylesheets for such errors.
Update: Microsoft Dynamics CRM 2016 is known to be affected because of
#0000 wrongly used for the text colour on a few elements.