User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; rv:1.7.3) Gecko/20040913 Firefox/0.10 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; rv:1.7.3) Gecko/20040913 Firefox/0.10 Try and open http://weatherley.net/firefox/foo.ppm it is just a text document but the 'ppm' extension causes firefox to show the 'What do you want me to do with this?' dialog: http://weatherley.net/firefox/foo.png If you choose to open with 'firefox.exe' and check the 'Do this automatically...' checkbox as shown in the above screenshot, when you press 'OK' firefox goes into a loop opening more and more browser windows until you kill the process with Task Mananger. Reproducible: Always Steps to Reproduce: 1. Try and open a file with a mystery extension 2. Say you want firefox to open it 3. Say you want step 2 to happen automatically 4. Press OK Actual Results: Firefox continuously spawns new windows. Expected Results: It should open the file as best it can and not keep passing it on to new instances of Firefox in the vain hope that one of them will figure out what to do with it.

*** This bug has been marked as a duplicate of 218257 ***