I really suggest to get rid of FF touching disk (cache). This is not only cookies but also ssl transactions, restore backups after browser crash, number of bookmarks backups and so on.
Cleaning just browser cache is not enough.
You can create user.js or directly edit about:config in FF. First method is preferable.
There is plenty of user.js available on the web. A lot of them going way above keeping system clean making FF very secure.
Here is an example of nice easy and secure user.js
https://github.com/arkenfox/user.js/
FF user.js file is OS agnostic so you can use it in Windows, Linux, BSD or Solaris.
Proper FF configuration is is better than cleaning after browser because you don't have to remember about it once set up. You can set up several FF profiles and experiment with user.js safely.
You can schedule log rotation and set up temp files in tmpfs so they will be gone after each system start. Again, no need to think about it once set up.
Remember that manual maintenance is not reliable. One exception is system update where is better to check if all the updates are necessary.
OS is just a tool that should make your life easier. It should not get in your way.
I bought my current laptop 3yrs ago. 3yrs ago I installed on it Linux. Never had to reinstall OS, never had an issue with shrinking free disk space temp files cache and so on. Same with my previous system: one installation in 6yrs. Configure OS once and forget about keeping it clean. Linux will do maintenance for you.