I think the reason I never originally went down that route, was because you have to supply a direct file location to launch a browser. So it would require users to edit it, or possibly have me implement the text-saving feature.
I *think* this is the command:
/shell_open <file>
Basically, for example:
C:\Program Files (x86)\Mozilla Firefox\firefox.exe
But I don't know if this slash command passes arguments too, ie:
C:\Program Files (x86)\Mozilla Firefox\firefox.exe -new-tab
http://google.com
You could give it a try by pasting it in-game chat and trying it out (you'll have to edit for your filepath as needed)
/shell_open "C:\Program Files (x86)\Mozilla Firefox\firefox.exe -new-tab http://google.com"
Experiment with the quotes being there or not. If you use chrome, just look up the command line arguments for it online.