https://support.mozilla.org/en-US/questions/1375244

I had the same problem as, for example, this: https://support.mozilla.org/en-US/questions/1375244 firefox (on linux) was unable to open a file browser to the local filesystem on clicking a website-provided button for file uploads, e.g. here https://video-converter.com/ I have seriously messed up with firefox settings over the years in order to safeguard my privacy, against all the attempts by firefox to infringe it. (Admitteddly, not as much as google chrome, safari and, got forbid, m$ edge). One of these fixes was to link the file/database content-prefs.sqlite (found in my firefox profile dir) to /dev/null. It was this that caused a problem with the file browser not showing. WOW! Once I deleted said file (linking to /dev/null). Firefox started and all was OK wrt the file brower. That caused me to create a script to be run before and after firefox launch, searching for all these privacy-infringing databases in my profile dir and erasing them. The steps to this are: 1) edit /usr/share/applications/org.mozilla.firefox.desktop and replace all Exec=firefox entries with Exec=/usr/local/bin/firefox-custom.sh 2) create a new file /usr/local/bin/firefox-custom.sh with this content #!/bin/bash CMD="firefox" if [ -x ~/bin/firefox-custom.sh ]; then CMD=~/bin/firefox-custom.sh fi echo "$0 : executing firefox with this command :" echo " ${CMD} $*" ${CMD} $* 3) create a ~/bin/firefox-custom.sh file with this content #!/bin/bash function eras { local f="$1" echo "erasing file '$f' ..." rm -f "${f}" } echo "$0 : on starting, erasing various sensitive firefox databases ..." while IFS='' read -r afil && [[ -n "$afil" ]]; do eras "${afil}" done <<< "$(find ~/.mozilla/firefox -type f -name 'content-prefs.sqlite')" echo "$0 : now executing firefox ..." firefox $* echo "$0 : on exiting, erasing various sensitive firefox databases ..." while IFS='' read -r afil && [[ -n "$afil" ]]; do eras "${afil}" done <<< "$(find ~/.mozilla/firefox -type f -name 'content-prefs.sqlite')" lanuching firefox now either from a desktop file (e.g. via Plank launcher) or from the command line: gio launch /usr/share/applications/org.mozilla.firefox.desktop runs the above script before and after firefox running. Disclaimer: the above script erases files in your profile directory, use at your own risk. Perpahs make a backup copy of your profile dir before.