Firefox's Inspector is using 8 digit hex codes for colors with transparency now. Those 8 digit hex codes and RGBa colors won't paste into the backend of b2evo(or any other cms as far as I know) but RGB can be used in stylesheets. There's no conversion from 8 digit to 6 digit of course but I did find an 8 digit hex to RGBa converter tool. The 8 digit hex isn't supported in all browsers (the usual suspects, IE, Edge, Opera mini and mobile) but RGBa has full support.
In FF Inspector >> Settings, you can change the "Default color unit" to RGBa but then all colors show as that regardless of opacity. Choosing Hex will give you all hex, either 6 or 8 digit. "As authored" is the default and shows whatever color units are used in the stylesheet(s).