Firefox not launching jupyter session properly

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I am running Ubuntu 21.10 on a Lenovo Thinkpad X1 Tablet. I use Firefox 98.0.2 (64-bit) as my browser. When I run sage -n jupyter file.ipynb A new tab opens in firefox with address file:///tmp/tmp9csp8qpp.html but Firefox reports

File not found

Firefox can’t find the file at /tmp/tmp9csp8qpp.html.

Check the file name for capitalization or other typing errors.
Check to see if the file was moved, renamed or deleted.

However the file does exist. ls -l /tmp/tmp9csp8qpp.html returns

-rw------- 1 brett brett 751 Mar 25 10:15 /tmp/tmp9csp8qpp.html

If I open the file in Firefox directly using Open File... from the File menu everything works fine.

When I run sage -n jupyter file.ipynb I get some other links in the terminal to use for opening the jupyter session in my browser:

To access the notebook, open this file in a browser:
    file:///home/brett/.local/share/jupyter/runtime/nbserver-101452-open.html
Or copy and paste one of these URLs:
    http://hamm:8888/?token=cb4036e78faba0faa3bd0d50b73cc7a94e302196c474d878
 or http://127.0.0.1:8888/?token=cb4036e78faba0faa3bd0d50b73cc7a94e302196c474d878

If I open the first of these, Firefox reports

Access to the file was denied

The file at /home/brett/.local/share/jupyter/runtime/nbserver-101452-open.html is not readable.

It may have been removed, moved, or file permissions may be preventing access.

However I have both read and write privileges for this file; ls -l /home/brett/.local/share/jupyter/runtime/nbserver-101452-open.html returns

-rw-rw-r-- 1 brett brett 667 Mar 25 10:15 /home/brett/.local/share/jupyter/runtime/nbserver-101452-open.html

I tried changing the privileges to include x but Firefox still will not open it.

Like above if I open the file in Firefox using Open File... from the File menu everything works fine.