Yeah, both the Macbook Pro 15s died on me, logic board issues baked into them due to a faulty batch. Bright side, data backed up, and another backup laptop – original 2006 black Macbook.
The last version of Firefox (v45 ESR) to run on it doesn’t support a semi-modern version of Adblock Plus, but there a silver lining there too – most simply don’t run or display on it. Found the original NoScript addon, and it’s relatively safe…. touch wood.