My daily backups of my personal account on a ubuntu-derived system are enormous. The first problem I found was the directory .cache, full of kinds of things that change daily and don't belong in a backup. I eliminated this directory from the backups, halving their size. So far so good. But the incremental backups are still huge, even on days where I've barely used the system at all. The next biggest questionable directory is .mozilla/firefox/05malccw.default-release and in particular .mozilla/firefox/05malccw.default-release/storage $ du -sh .mozilla/firefox/05malccw.default-release/storage 2.2G .mozilla/firefox/05malccw.default-release/storage It's pretty clear what program creates this and regularly changes it contents. Examining the files suggests that most or all of them are useless in a data-recovery type situation. But I'm not sure. What's in this directory? Will the path change when I update to a new version of firefox, using normal ubuntu tools? Is there an rsync pattern I can use to identify all possible directories with this function, so as to teach my backup script to ignore not only the current directory, but the one I'll get when I next update firefox? Are there other directories created/populated by firefox that shouldn't be in backups, besides .mozilla/firefox/05malccw.default-release/ and .cache/mozilla ? Note that I'm on an ubuntu derivative, using the packages from the distro repositories; it's more than possible that paths are determines at build time, by the people who configure and build those packages.