This issue occurs with password protected files from both Writer and Calc, that I have seen.
I regularly use a password protected Calc file. Often, though not always, I am unable to enter data into cells if Firefox is already running. However, I can open and edit unprotected files.
To work around the issue, I must close Firefox and the password protected Calc file. Then reopen the Calc file and data input works as expected. I can even reopen Firefox and everything continues fine.
Can anyone duplicate this issue, or better yet, provide a solution?
Firefox Versions at least 35 - 37.0.2
Libre Office Version 4.1.62