Same for me here since FF 95.0. I have a long-running test application that at intervals chunks out a test-result that needs to be appended to the overall report. Instead of re-saving the entire report over and over again, I safe the newest test-result separately, and then recreate the 'index' report. The 'index' report is supposed to load all partial results, whereby the partial results get loaded by a little java-script. The javascript fetch command as shown below always worked for me, but not anymore.

PS: Just as the user above I double checked that privacy.file_unique_origin is still false (not the Firefox default)

< !DOCTYPE html> < html>

 < head>
   < meta charset='UTF-8'>
   < link rel='stylesheet' href='lt.css'>
   < script type='text/javascript' src='lt.js'></script>
 < /head>
 < body>
   < div class='js-include' data-name='test4.16.html'></div>

   < div class='js-include' data-name='test4.17.html'></div>

   <script>
       const components = document.querySelectorAll('.js-include')
       const loadComponent = async c => {
           const { name } = c.dataset
           const response = await fetch(`${name}`)
           const html = await response.text()
           c.innerHTML = html
           const tabs = c.getElementsByClassName('defaultOpen');
           for(const i of tabs)
               i.click();
       }
       [...components].forEach(loadComponent)
   < /script>
 < /body>

< /html>

I saw in a post on Reddit (by a person familiar with the internals) that privacy.file_unique_origin was removed from the code in Firefox 95.

You might have a lingering custom preference, but the icon at the right end of the bar will have changed from a reset arrow to a trash can.

For previewing purposes, you could work around this by running a web server on your computer. I'm not sure about the index generation script; that might need to be done using some other tool. Or another browser if it is less restrictive than Firefox.

History note: This preference was introduced in Firefox 68 to address CVE-2019-11730 to resolve the issue that all local files in the same folder had "same-origin" privileges to one another's content and data.

This pref got removed in Firefox 95.

• 1732052 - Remove pref privacy.file_unique_origin
• 1745987 - Browsing local files no more possible

(please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html)