Stop the search once started or at least control when it "starts"
Add a stop/start button to the search process.
If you change the criteria, it immediately starts searching for that criteria before you get a chance to change some of the other parameters.
Worst case scenario it eats up all the memory and crashes SSMS if you search against "All Databases" on a production server.
Give some control back to the UI.
Hard to believe this is not implemented yet, rookie design mistake not to include a STOP button..