I logged in my GitHub/StackOverflow etc accounts with my personal accounts in chrome personal account . in the work user, I logged with my work accounts. the chrome is the default browser in my machine. what I need is that when there is a link has posted on slack I have this option to select with which user I want to open it. it could happen in the slack level and the second level could be browser level to ask which user I want to open the link before opening it.
When Slack responded, they were not able to inject the payload I suggested. The Rocket socket was a bit messy, due to all the markers, IDs and counters that had to be properly set for the proxy modification to work properly. They also thought the issue was present inside slack-files.com which was not the case, the XSS only triggered on [teamname].slack.com.