although I think most I2C accessories to Arduino assume internal pullups
when I use standard firmata to check
Yes if you look at the schematic of the Olimexino you will see if has pull up resistors on these two lines. By the resistors R12 & R13 is a round pad with a small link, you can cut this link to remove the pull up resistors.There are no such resistors on the Leonardo.
Quotealthough I think most I2C accessories to Arduino assume internal pullupsAn arduino needs external pull up resistors as the internal ones are too high a value.