Normally modern SSDs have a theoretical write/read limit of 10,000 to 100,000 cycles (
P/E cycles), meaning if you had a 64 GB SSD and its cycle limit would be 10,000, you would have to write 625 TB to it, which would be 351 GB per day everyday for the next five years. Assuming those numbers vary and it would only be a tenth of that, it would still mean 35 GB per day, which under normal usage no average computer consumer does, not even with temporary files.
In other words, it is not necessary to do what you want to do just to save some write/read cycles (typically one cycle takes more than one day on a 64 GB SSD, even more than a week on bigger ones, unless you constantly write to it, in which case, moving Firefox or other applications onto an external HDD will not help anyway).
SSD endurance
PS: Normally applications use the Macintosh HD / Users / YOU / Library / Application Support / folder to write and read temporary files, thus it would make less sense to start applications from an external HDD (Firefox 11 is 80 MB in size, you would have to start it 52,428,800,000 times to fulfill 10,000 cycles on a 64 GB SSD - that is more than 52 billion times, 332 times per second over five years, SSDs can't even read that fast).
----------
Looks like I spoke too soon. Firefox, even though installed the USB drive still stores the cache in the User/myname/Library/Application Support/Firefox folder.'
lol @ moving entire applications folder. Yeah, I'm not that paranoid yet. I tried PortableApps on a USB drive till it got so hot it smelled like burning plastic and my Mac said it was using too much power and disconnected it. lol
Sorry, it took so long for the reply to explain everything (had to do some research on numbers and do the the calculations), but you don't need to do that. Doing that would defeat the purpose of the SSD and limit you to USB 2.0 speeds and slow seek times. Isn't the SSD one of the positive things about the
MacBook Air?
----------
Now I am confused:
SSD Life Remaining, am I understanding you wrong?
