Trying an upgrade from 2.2.15 to 2.3.0 B2; upgrade itself went well but am getting an error when trying to enter any value in the ACP Additional icons to include in sprites option.
Appears the correct reference for that icon would be fa-acorn and not fa fa-acorn for the default icon variant. Although, I would hope it would not error out either way.
Thank you for reporting this issue, it has now been resolved. We are aiming to include any changes that have been made in a future XF release (2.3.0 Beta 3).
Change log:
Fix error when attempting to save additional icons option