By I had problems getting Sahi to work properly with Firefox 5 when using it with Behat to perform in-browser testing on Mac OS X.
Moving the Firefox 5 .app to a subfolder in the /Applications directory, and installing Firefox 3 at the root level of /Applications still led to Sahi firing up Firefox 5.
If you have this problem, the solution is to edit the SAHI_ROOT/userdata/config/browser_types.xml file, and put the FULL path to the browser in thedirective – eg:
open -n -a /Applications/Firefox3/Firefox.app(I have moved my Firefox 3 to a subfolder, and returned 5 to the root of Applications).
This works beautifully.