我编写了一个脚本来自动从网络下载文件，如下所示：
#Automatically download files to a given folder profile settings
#---------------------------------------------------------------
profile = Selenium::WebDriver::Firefox::Profile.new
profile['browser.download.dir'] = 'C:\Documents and Settings\My Documents\userdata\Rubydownloads'
profile['browser.download.folderList'] = 2
profile['browser.helperApps.neverAsk.saveToDisk'] = "application/pdf,application/x-pdf,application/acrobat,application/vnd.pdf,text/pdf,text/x-pdf,image/jpeg,image/pjpeg,image/gif,image/bmp,image/x-windows-bmp,image/tif,image/x-tif,image/tiff,image/x-tiff,application/tif,application/x-tif,application/tiff,application/x-tiff"
profile['browser.download.manager.showWhenStarting'] = false
driver = Selenium::WebDriver.for :firefox, :profile => profile
但我的不好，一些.tif,.tiff and .pdf仍然错过而没有被下载。可以做到吗，比如说 - 如果mime type在上述配置文件设置中找不到合适的，那么脚本应该将其添加mime到浏览器设置中，以继续下载？
请在这里帮助我。