This is probably going to be based more on how your OS works but I will try to answer the question.
First, the easy one. In Firefox or any other normal browser, you can go to file:/// to browse your local filesystem. This function is not available in Tor Browser if you don't have access to the / directory.
The error is:
Access to the file was denied
In the Tor Browser profile directory (the directory where you normally could find the prefs.js file had it been there - but it doesn't need to actually pre-exist) create a file named user.js with the following contents:
In the search bar, type about:config and accept the risk to continue.
Then find the variable network.dns.blockDotOnion and change it to false. If your network configuration was done correctly, firefox should now be able to resolve .onion addresses.
The easy answer is that you don't. The Tor Manual says:
Tor Browser must be kept updated at all times. If you continue to use
an outdated version of the software, you may be vulnerable to serious
security flaws that compromise your privacy and anonymity.
Tor Browser will prompt you to update the software once a new version
has been released: ...