If you can get a petabyte of r/w out of an SSD then 12 GB/day (of writes only) will exhaust the device in 228 years (1 PB * 1000 TB/PB * 1000 GB/TB / 12 GB/Day / 365 Days/Year).
If there is also an associated 12 GB/day of reads then half that estimate (unlikely to be equal due to the nature of the cache). Either way -- not a significant degradation.
Edit: Degradation or not -- i'd personally rather have my drive resources available. In the context switch from firefox the cache process could interfere with loading other data.
It was the 840 Pro that went 2.4 terabytes during a drive test that ended in 2015[0]. That was a 21nm tech. I think the endurance is better than you think.
afair this test was run 24/7 with no power down time. Earlier test (the one with 830? I think he moved computer mid test and had to power everything down) showed drives look healthy until you let them sit offline for a while, then it turns out all data evaporated.
840 is especially broken and dramatically slows down when you dont touch the data for >month. The "fix" is firmware silently rewriting everything in the background burning thru the rewrite cycles.
If there is also an associated 12 GB/day of reads then half that estimate (unlikely to be equal due to the nature of the cache). Either way -- not a significant degradation.
Edit: Degradation or not -- i'd personally rather have my drive resources available. In the context switch from firefox the cache process could interfere with loading other data.