Thank you for the review! The behavior/bug you describe is not related to SingleFile but rather to Firefox. The only thing that could be causing this problem from my point of view would be related to the settings in the “File format” section of the options page in SingleFile. You have to make sure the file format is “HTML”. You can also reset the settings to see if it fixes the issue.

UPDATE - I'm glad to hear the issue is resolved! 😊