title: Selenium IDE fails to open a test suite (no file open dialog)
body: <p>I am not able to access the file open dialog in Selenium IDE 2.9.1 (Firefox 48.0, Win 10). File > Open results in this error message: </p>
  
  <pre><code>There was an unexpected error. Msg: NS_ERROR_FILE_UNRECOGNIZED_PATH: Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsILocalFile.initWithPath]
  Url: chrome://selenium-ide/content/file-utils.js, line: 32
  FileUtils.getFile@chrome://selenium-ide/content/file-utils.js:32:5
  showFilePicker@chrome://selenium-ide/content/tools.js:102:31
  Application.prototype.loadTestCaseWithNewSuite@chrome://selenium-ide/content/application.js:259:20
  Editor.prototype.loadRecentTestCase@chrome://selenium-ide/content/editor.js:489:5
  Editor.controller.doCommand@chrome://selenium-ide/content/editor.js:366:9
  goDoCommand@chrome://global/content/globalOverlay.js:100:7
  oncommand@chrome://selenium-ide/content/selenium-ide.xul:1:1
  </code></pre>
  
  <p>File > Open Test Suite results in a shorter error: </p>
  
  <pre><code>error loading test suite: [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsILocalFile.initWithPath]"  nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)"  location: "JS frame :: chrome://selenium-ide/content/file-utils.js :: FileUtils.getFile :: line 32"  data: no]
  </code></pre>
  
  <p>Does anyone have a clue what's wrong here?</p>