Problem
You are trying to load a script from a local file into a page displayed in Firefox (as can sometimes be useful for testing).
Firefox reports an error such as
Error: Permission denied to access property ‘document’
Error: Permission denied to access property ‘local’
Solution
This problem is caused by a security restriction that should normally be in place. However, you can temporarily disable this security feature as follows:
- Enter the address ‘about:config’ in your Firefox
- Search for ‘strict_’
- Double click on the value column for the preference ‘security.fileuri.strict_origin_policy‘ to switch it from ‘true’ to ‘false’.
Remember to reenable the policy once your tests are done!
Code of Joy 
This setting did not fix the issue in FF 48.02. Adding in the web link that gave the error to the Java security setting as trusted also did not help.
Hmm, what error message did you get exactly? Java Security settings should not matter as long as the local file you are trying to access won’t be a Java Applet which I guess is quite a special case? Anything helped you in the end?