This is a pretty good idea but I feel like it exposes some of the shortcomings in our modern UI stack and file browsers. Users using the tools the OS provides to solve problems like this should be encouraged, however the separation between the file browser UI and the web browser UI feels like it creates a certain amount of inertia to using such a solution. If my UI had enough customizability that I could easily do something like attach a slide out drawer of a file browser view to my web browser windows, I feel like I'd be much more free to experiment with mixing and matching the various tools at my disposal and using my own solutions to problems like this.