If hauling firewood is your only reason for a larger bucket, consider getting a piece of plate steel bent to conform to the inside of your bucket that extends like WranglerX's fork additions. Make it fit the bucket, and drill a single hole in each side of it to pin to your bucket, or if you don't want to drill your bucket, consider a chain or other method to keep it attached when loaded. Sides and a flat bottom will allow more wood to be stacked in the extended bucket, probably more than a wider bucket will gain.
David from jax