OK so since I wasn't able to find a solution here and wanted to share the solution I found since so many folks seem to be having this issue despite so many of them being …
OK so since I wasn't able to find a solution here and wanted to share the solution I found since so many folks seem to be having this issue despite so many of them being 'resolved' and 'archived' with non satisfactory solution, let me share what I found. This applies for those who have already tried these steps:
- If you can access the site that gives you this error in Firefox but no issues in another browser; - If you've cleared the cache and you still get the error; - If you've deleted all cookies and still get the error; - If you've tried starting Firefox in Safe Mode to temporarily disable your addons and still get the error,
Try this: - in the address bar type "about:serviceworkers"; a whole list of these hidden code/cookie snippets should appear in the page. I was shocked by the shear amount of them and their privacy implications >:-( - click "unregister" to remove them one by one - restart your browser.
After restarting, the problem disappeared. In my case, a corrupted 'serviceworker' was preventing me from accessing gmail.
Upon further reading, one learns that it's some kind of cache and that it helps accessing websites. Also, that it gets rebuilt as required. Finally, that this 'feature' can be disabled by turning the about:config value dom.serviceWorkers.enabled to false.
Hope this helps someone, and sorry if the formatting looks awful, I have no idea why my bulleted list doesn't show as it does in the editor.