This problem starts on firefox version 8.2.0 esr and after such as 39, 39.0.3 ..., the version 38.1.1 esr and before work fine, no problem at all. problem is when the website using Unity Player call a javascript function, the modal dialog pops up, and the it hangs, mouse click don't work, the whole web site is frozen. the only way to 'fix' it is move the mouse to outside browser, and move it back, the mouse click works again. steps to test: 1. Go to website, http://www.egowall.com 2. Register as a new user by click Join Now button. After email confirmed, log on to the site. 3. Connect to the facebook is an optional. 4. Click on START PLAYING 5. Select one of the houses and click Buy, after bought a house, click DONE on the next page. 6. Click on Enter home. hit Continue button when shown. 7. After entered the home, move mouse to the lower corner. there are 4 small icons, click on Multimedia icon (mouseover to see it) 8. A convey belt will display. select the suitcase at left hand side. 9. Click on the suitcase and a black wood box will shop up. click on the box. 10. A photo banner will pops up. 11. click on ADD PHOTO on the lower right hand side of the pop-up banner. 12. When the Add Photo dialog pupped up, the BROWSER HANGS, MOUSE DO NOT WORK AT ALL, NOT CLICK 13.Move mouse to outside the browser and back. the dialog works. tested firebox versions and results: Y= has the hanging problem N= has not the hanging problem 40 8/12/2015 Y 39.0.3 8/6/2015 Y 39 7/1/2015 Y 38.2.0 esr 8/6/2015 Y 38.1.1 esr 8/6/2015 N 38.1.0 esr 6/25/2015 N 38.0 esr 5/5/2015 N 38.0.6 6/9/2015 N OS version: windows 7.0 Platform: varies P.C. It is only happens on firefox with newer version, all other browsers have no such problem. Thank you for the help.