Dear WeatherCat users who never seem to have enough memory,
A number of us has noticed a slow parasitical memory use that eventually consumes all the available memory on a Mac. It certainly exists on Mavericks, Yosemite, and El Capitan. Supposedly there have been improvements in macOS Sierra that perhaps have resolved these problems.
Given the number of "memory cleaner" applications on the Mac App store, it is clear that this is a common problem. Alas those programs may not be the best medicine. There is a command line alternative called purge. It needs to be invoked in the terminal as a super-user like this:
There is one unavoidable hassle associated with this: having to type your password at every invocation.
There is a lot of debate about whether this is a good idea or not, but I discovered that using the purge command has a very surprising effect after running any of the Mozilla based applications like Firefox, Waterfox, or Postbox. Even if these applications are on the order a few hundred megabytes, purging the caches typically recovers around a gigabyte of RAM!! The free memory cleaner app I was running could not recover anywhere close to the same amount of memory.
My suspicion is that there are bugs in the Mozilla code that cause it to be unable to cache data efficiently. As a result, repeated use of these programs cause the caches to grow very rapidly and the data doesn't get reused correctly. Efficiently, the caching is basically worthless and the RAM on your computer is rapidly consumed. Since I use Waterfox (formerly Firefox) and Postbox a great deal during the day, I was being forced to reboot as often as once a day. Through periodic purging, I could go as long as 2 weeks without rebooting.
As noted by board member Weatheraardvark, Safari appears to be more efficient in memory use and does not appear to generate the amount of cached data Mozilla family appears to generate. That is a more memory friendly alternative. However, if you are addicted to the Mozilla family of products, periodically running the purge command may be a reasonable compromise to avoid rebooting your computer all the time.