Wouldn't matter, if the attack works as described. It's already exfiltrating data cross-process due to the processes sharing a resource (the CPU cache). It do

Wouldn't matter, if the attack works as described. It's already exfiltrating data cross-process due to the processes sharing a resource (the CPU cache). It doesn't matter whether the processes are the same browser or different browsers. Now the actual "cache fingerprint" of a particular pageload might be different in different browsers, so it might not be possible to differentiate "site A loaded in Firefox" and "site B loaded in Chrome". Or it might be, and then you know not only what sites the user is visiting but what browser they're using to do it...