hi pioj,
there is no doubt that
/opt/.xfiletool.lst is the first tool to keep your backup-file slim & beauty...
but for programs like browsers and mail-clients i use an different approach:
for firefox (and its clones) and thunderbird i use a standarized file-set that is loaded everytime and i don't backup the "exploded, used" directory. only in thunderbird i backup the popstate.dat that logs all previous downloaded mails to prevent the download of old mails. from time to time i adjust some config files of my standard-file-set for my convience and for getting ahead in terms of development and security.
with this standard-file-set i keep my backup at tiny 1,3 mb with endless configuration files and individual scripts for almost every program and tool i need for my daily life (although some plugins take more than 1 mb)...