The daily backup of my personal data includes my Firefox profile. However, this profile is quite big (mine is 1.4 GB) and changes daily, which increases the size of my backup significantly.

When looking at the contents of the profile, the directory storage/default (in ~/.mozilla/firefox/*.default on linux) was by far the largest one with about 700 MB. Inside, you will find

  1. Configuration data of extensions in directories named moz-extension*,
  2. General configuration data in about+newtab and moz-save-about+home, and
  3. Cached website data in directories starting with http (e.g. https+++stackoverflow.com).

In my opinion, there is no need to backup cached website data. So I configured my backup software to exclude this data and all temporary data:

%HOME%/.mozilla/firefox/*.default/storage/default/http*
%HOME%/.mozilla/firefox/*.default/storage/temporary/*

Depending on the backup software, the string %HOME% may need to be replaced.