Hi worlebird, there's no convenient way to use a file:// URL for your new tab page, as you've discovered.

As noted in the other thread where you posted, here in support we work with the Firefox we have today and can suggest relevant features, available settings changes, and workarounds such as add-ons. If those do not suit your needs, you can submit comments and suggestions through one or more of the following links:

• Feedback: https://qsurvey.mozilla.com/s3/FirefoxInput/
• Discourse: https://discourse.mozilla.org/c/firefox-development
• Reddit: https://www.reddit.com/r/firefox/
• Twitter: https://twitter.com/firefox
• Facebook: https://www.facebook.com/Firefox

In Firefox 58 and earlier, there was a method to use a configuration file to modify the new tab page at startup. However, that was supposed to stop working in Firefox 59, so the method in this thread may be obsolete: I want to open new tabs in a local page.

If you wanted to run the script by hand in the Browser Console:

(1) One-time setup

(A) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(B) In the search box above the list, type or paste devt and pause while the list is filtered

(C) Double-click the devtools.chrome.enabled preference to switch the value from false to true

Be cautious about the scripts you run!

(2) Script to override the new tab page for the current session

You can open the separate Browser Console window using either:

• "3-bar" menu button > Web Developer > Browser Console
• (menu bar) Tools > Web Developer > Browser Console
• (Windows) Ctrl+Shift+j

Paste the following script after the caret (»), edit about:newtab to the desired URL, and press Enter to execute it:

var {classes:Cc,interfaces:Ci,utils:Cu} = Components;
try {
  aboutNewTabService = Cc["@mozilla.org/browser/aboutnewtab-service;1"].getService(Ci.nsIAboutNewTabService);
  aboutNewTabService.newTabURL = 'about:newtab';
} catch(err){
  Cu.reportError(err);
}

More info on the Browser Console: https://developer.mozilla.org/docs/Tools/Browser_Console

worlebird said

• Go to "about:preferences".
• Select "Home".
• Under "New Windows and Tabs", see options "Homepage and new windows".
• Choose "Custom URLs...".
• Enter a local HTML file in the address box.

Now, when you open a new Firefox window, the local HTML file will open as your homepage. This is good.

However, if you open a new tab, your selected homepage will NOT load...

See This Post.

~Pj

Note that probably using only this line will work in the Browser Console:

• aboutNewTabService.newTabURL = "about:newtab";
• "3-bar" menu button or Tools -> Web Developer

This is a getter/setter, so you can check the curren newTabURL setting via:

• aboutNewTabService.newTabURL;