Soon i will be able to try out a Firewalla gold and i want to use it as router but i do not want to get rid of the RB5009.
I have a fiber connection from my ISP and they at the time installed a Huawei mediaconverter which i immediately removed.
Currently i have my RB5009 connected to the fiber cable directly with a SFP, i want to keep it this way but i do not want to use it as a router when i try out the firewalla box.
I just want to use it as mediaconverter because the rb5009 is powered by a POE switch and the huawei would eat up another powersocket which i do not have.
Can i use the rb5009 just as a simple “Mediaconverter” so i can plug in the firewalla (which does not have a sfp) with rj45 in my mikrotik.
Expensive media convertor … but yes, quite possible.
Temporarily 
Any idea on how to exactly do this?
Put SFP and ether in one bridge.
Nothing else to be done, I would think.
absolutely viable
have 2 4011 in that configuration and it works quite well.
those 2 4011 are installed temporarily to insert a “tap point” for a POC setup for a palo alto IDS/IPS solution. working transparently and at wirespeed so far
so 5009 surely will handle the load
just create a bridge and add the SFP and RJ45 interface without vlan-filtering
adjust the MTU of the bridge to your needs and you are good to go