Hi Marcos,
Just a quick update: Ive just tried another test. First, I installed version FF52, then I disabled/renabled SSL filtering, and then I did an auto upgrade to FF53.0.2. SSL filtering worked.
Then, I uninstalled this instance of FF, kept the profile (so that the SSL cert remains in the cert8.db), and reinstall FF53.0.2. Again, SSL filtering worked as expected.
Finally, I uninstalled the FF app and removed the profile, and reinstall again FF53.0.2. SSL filtering, as expected, stops working.
Cheers!