How do I set the default Firefox zoom level for *local* files?

Question

Every time I open a new local file, the zoom level is reset to 100%. Is there a way/extension to make the default a different zoom percent?

It'd be even better (but not required) if I could set this per file path. e.g., all C:/docs files open at 500%. The rest would be at 100%.

Answer 1

I had the same problem. Some options:

• Install Tampermonkey, this is a Firefox extension to run your own Javascript code on websites of your choice.

  Then you can make a script like this:

  // ==UserScript==
  // @name         Zoom Qt docs
  // @match        file:///C:/qt/Docs/*
  // @grant        GM_addStyle
  // ==/UserScript==
  
  var scale = 1.2;
  
  var css = `
      html {
          width: ${100 / scale}%;
          transform-origin: top left;
          transform: scale(${scale});
      }
  `;
  
  GM_addStyle(css);
  

  Text rendering seems to be worse when using this instead of normal browser zoom (Firefox 108), so I do not recommend this.

• Write a Firefox extension to set the browser zoom level, this seems to be possible with the browser.tabs.setZoom function. I was hoping I could call this function from a Tampermonkey script, but that seems to be impossible.

• Run a local web server. Let it listen on 127.0.0.1 so it doesn't allow connections from other computers. To have different zoom settings for different sites, make up a hostname for every site and add the hostnames to your hosts file. Let them all point to 127.0.0.1.

  I ended up installing NGINX with this configuration:

  events {}
  
  http {
      server {
          listen 127.0.0.1:80;
          location / {
              root "c:\\";
              autoindex on;
          }
      }
  }