Firefox and therefore TenFourFox are hard on SSD's because of the frequency and amount of data that it caches (ie: writes to disk). The cause of this activity is the frequency that open pages are saved to disk - the saved information is used to recover open pages in the event that Firefox crashes. By default every page / tab that's open is written to disk every 15 seconds, regardless if the page has changed (since the last write) or not. Two options to reduce SSD wear are (1) change the interval information is saved and (2) move the save location to a different location (ie: spinning hard drive). Option 1 is documented in this post -> LINK. Option 2 - move the save location is documented below: Firefox stores the open page caches in the Firefox profile directory. In the ~/Library/Application Support/Firefox directory there's a profiles.ini file. One of the lines in profiles.ini, IsRelative, tells Firefox if the profiles path is relative or independent of where the profiles.ini file is located. By default it is relative and set to one (1). By changing this to a zero (0) and editing the line beginning with Path to a valid fully qualified path you can relocate Firefox's profile. Here are copies of the relevant lines from my original and edited profiles.ini file: --<ORIG>-- IsRelative=1 Path=Profiles/61ovfrgl.default --<EDITED>-- IsRelative=0 Path=/Volumes/Files/temp/Firefox-Profiles/61ovfrgl.default Important Note You need to manually copy (or move) your profile directory to the new location. If you don't Firefox will create a new profile and none of your customization (add on's, settings, tweaks, etc) will be used. In case you forget to move your profile directory simply shutdown Firefox, delete the new profile directory then copy / move your profile directory.