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

I installed Rust on my laptop and want to browse to the documentation which is installed at file:///home/lochlann/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/share/doc/rust/html/intro.html. I try to open this in Firefox and this fails with the message: Access to the file was denied The file at /home/lochlann/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/share/doc/rust/html/intro.html is not readable. It may have been removed, moved, or file permissions may be preventing access. I have read permissions on the file. No matter, it fails. I try to open the file using Firefox and navigate the directory structure rather than typing in the location. The file opens in the browser, the location is listed as file:///run/user/1000/doc/1f137432/index.html. Can you explain to me why Firefox cannot render a file that is where i put it and has appropriate permissions yet can render the same file where I did not put it? I have always been a fan but this looks more like a virus than I am comfortable with.