It's pretty sure an issue with the cooker itself as it might only use the very old 802.11b WiFi standard. This standard is not supported by the Vodafone Station anymore as it results in huge speed issues.
It has nothing to do with a firewall if the device cannot connect to the WLAN.
As I said - those devices usually only have an 802.11b WiFi module built-in - even if they write "compatible to 802.11b/g/n" - as 802.11g/n devices are required by the corresponding standard to support the slower 802.11b speeds, but there is no requirement for routers/base stations to have this compatibility mode enabled all the time. It might be enabled - but there is no requirement that is has to be enabled.
And as far as I know, Vodafone and the device vendor decided NOT to enable this compatibility mode - therefor 802.11b-only devices cannot connect to the WiFi anymore. Thus meaning your rice cooker will not be able to connect to the WiFi at all.