A Bug in Firefox For Android will force to download all webpage instead to loads its contents and can lead to Same-Origin Policy Bypass
1) ClickMe1 (A new tab will be opened)
-a) Wait until that a [Warning: Unresponsive script] MsgBox appears and Click on its "Continue" button
-b) Go back to the tab of this WebPage (View Video demo in attachments)
Close Firefox and Reopen Firefox (we can use a crash Bug to close Firefox without user interaction)
and go to the downloaded file open-me.html into the download folder:
file:///storage/emulated/0/Download/open-me.html