Firefox Linux: Get tabs to open with startpage

July 09, 2020

Boy, this took some searching, but I finally got it.

Enable userChrome using the instructions here
The directory you care about is /usr/lib/firefox, not /etc/firefox nor .mozilla, so cd into that directory
Add the following files including the comments at the top

// /usr/lib/firefox/firefox.cfg
var {classes:Cc,interfaces:Ci,utils:Cu} = Components;

/* set new tab page */
try {
  Cu.import("resource:///modules/AboutNewTab.jsm");
  var newTabURL = "file:///absolute/path/to/your/startpage/goes/here/index.html";
  AboutNewTab.newTabURL = newTabURL;
} catch(e){Cu.reportError(e);} // report errors in the Browser Console

Note that you must replace the file:///absolute/path/to/your/startpage/goes/here/index.html above

// /usr/lib/firefox/defaults/pref/autoconfig.js
pref("general.config.filename", "firefox.cfg");
pref("general.config.obscure_value", 0);
pref("general.config.sandbox_enabled", false);

That 3rd line disabling sandbox is important.

Now you can pick out a slick startpage or create your own. Personally I really like this one, but I made a few changes.

MaterialFox is also a nice theme to pair with.