Hi all! I've figured out what changes makes firefox when you start it with -setdefaultbrowser switch. Here's the list Windows Registry Editor Version 5.00 [HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main] "Check_Associations"="No" [HKEY_LOCAL_MACHINE\Software\Microsoft\Internet Explorer\Main] "Check_Associations"="No" [HKEY_CLASSES_ROOT\ftp\DefaultIcon] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE,1" [HKEY_CLASSES_ROOT\ftp\shell\open\command] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE -url \"%1\"" [HKEY_CLASSES_ROOT\.htm] @="FirefoxHTML" [HKEY_CLASSES_ROOT\CHROME\DefaultIcon] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE,1" [HKEY_CLASSES_ROOT\CHROME\shell\open\command] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE -url \"%1\"" [HKEY_CLASSES_ROOT\.html] @="FirefoxHTML" "Content Type"="text/html" [HKEY_CLASSES_ROOT\.shtml] @="FirefoxHTML" [HKEY_CLASSES_ROOT\.xht] @="FirefoxHTML" [HKEY_CLASSES_ROOT\.xhtml] @="FirefoxHTML" [HKEY_CLASSES_ROOT\FirefoxHTML\DefaultIcon] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE,1" [HKEY_CLASSES_ROOT\FirefoxHTML\shell\open\command] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE -url \"%1\"" [HKEY_CLASSES_ROOT\gopher\DefaultIcon] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE,1" [HKEY_CLASSES_ROOT\gopher\shell\open\command] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE -url \"%1\"" [HKEY_CLASSES_ROOT\HTTP\DefaultIcon] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE,1" [HKEY_CLASSES_ROOT\HTTP\shell\open\command] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE -url \"%1\"" [HKEY_CLASSES_ROOT\https\DefaultIcon] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE,1" [HKEY_CLASSES_ROOT\https\shell\open\command] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE -url \"%1\"" [HKEY_CLASSES_ROOT\MIME\Database\Content Type\application/x-xpinstall;app=firefox] "Extension"=".xpi" [HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla\Desktop] "SOFTWARE\\Classes\\.htm"="htmlfile" "SOFTWARE\\Classes\\.html"="htmlfile" "SOFTWARE\\Classes\\HTTP\\DefaultIcon"="%SystemRoot%\\system32\\url.dll,0" "SOFTWARE\\Classes\\HTTP\\shell\\open\\command"="\"C:\\Program Files\\Internet Explorer\\iexplore.exe\" -nohome" "SOFTWARE\\Classes\\HTTPS\\DefaultIcon"="%SystemRoot%\\system32\\url.dll,0" "SOFTWARE\\Classes\\HTTPS\\shell\\open\\command"="\"C:\\Program Files\\Internet Explorer\\iexplore.exe\" -nohome" "SOFTWARE\\Classes\\FTP\\DefaultIcon"="%SystemRoot%\\system32\\url.dll,0" "SOFTWARE\\Classes\\FTP\\shell\\open\\command"="\"C:\\Program Files\\Internet Explorer\\iexplore.exe\" %1" "SOFTWARE\\Classes\\GOPHER\\DefaultIcon"="%SystemRoot%\\system32\\url.dll,0" "SOFTWARE\\Classes\\GOPHER\\shell\\open\\command"="\"C:\\Program Files\\Internet Explorer\\iexplore.exe\" -nohome" "SOFTWARE\\Clients\\StartMenuInternet\\"="IEXPLORE.EXE" [HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet] @="FIREFOX.EXE" [HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet\FIREFOX.EXE] @="Mozilla Firefox" [HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet\FIREFOX.EXE\DefaultIcon] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE,0" [HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet\FIREFOX.EXE\shell\open\command] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE" [HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet\FIREFOX.EXE\shell\properties] @="Firefox &beállításai" [HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet\FIREFOX.EXE\shell\properties\command] @="C:\\PROGRA~1\\MOZILL~1\\FIREFOX.EXE -preferences" [-HKEY_CLASSES_ROOT\ftp\shell\open\ddeexec] [-HKEY_CLASSES_ROOT\gopher\shell\open\ddeexec] [-HKEY_CLASSES_ROOT\http\shell\open\ddeexec] [-HKEY_CLASSES_ROOT\https\shell\open\ddeexec] NOTE: the first 2line is for not to look up internet explorer if it isn't the default browser. It doesn't delete any dependences for ie. I've just collected the changes made by firefox Cheers