I have a Linux box (Debian 9) with 2 NICs (Ethernet & Wifi) and they both connect to different networks. Is it possible to configure the browser to use the Wifi NIC and all the rest of apps to use the Ethernet NIC (or choose which traffic should go through which NIC) ?
Based on @dirkt comment, it can be done using namespaces.
If you are not using physical NICs, that can be done with
1- Create a new network namespace :
ip netns add net1
2- Move your NIC to that new namespace :
ip link set NIC netns wifi // replace NIC
3- Start the app inside that new namespace and it will use only the NIC moved inside that namespace :
ip netns exec net1 CMD args ...
If your NIC is a physical card then a more elaborated process should be used, the following link provides more details: Move physical NIC to a different namespace