This is not really a problem with Tor, but within Firefox. One of the certificates which Firefox uses for signing of add-ons is expired. They write about it in their bugtracking system: https://bugzilla.mozilla.org/show_bug.cgi?id=1548973
Hopefully this will fixed within the next hours.
Tor also has the entry #30388 in their bug tracker.
So basically we ...
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
copy %userprofile%\desktop\Old Firefox Data\profile.default to %yourTORpath%\Browser\TorBrowser\Data\Browser and rename to profile.default-1234567891011. Actually suffix is random,
I guess, but I copied it from another profile in this directory. Then edit profile.ini in the same directory and put it as following: