I've got a local HTML file that I use as a home page and I'd like to replace the new tab page with it as well. The recent update (76), have broken my previous method of doing this. I did this using an autoconfig file described by user cor-el's answers to the same question: https://support.mozilla.org/en-US/questions/1251199. After the recent update, my browser fails to read the .cfg on startup and tells me that each time I open Firefox ('failed to read the configuration file'). For transparency, the code in that .cfg file looks like this: // Do not remove this comment var {classes:Cc,interfaces:Ci,utils:Cu} = Components; var newTabURL = "file:///path-to-my-page/index.html"; aboutNewTabService = Cc["@mozilla.org/browser/aboutnewtab-service;1"].getService(Ci.nsIAboutNewTabService); aboutNewTabService.newTabURL = newTabURL; Not sure how to put that in a code format on this forum. If anyone has any idea why the recent changes have broken this or a way to fix it, I'd appreciate it. Edit: I've figured out it fails on the last line, as commenting that out causes it to no longer fail to read the config file. Can you not set the newTabURL anymore? Has it been renamed to something else?