I am starting to think a lot of information that people share is outdated 
I just did a clean install of Fedora Silverblue 38 via USB stick, then ran rpm-ostree upgrade, rebooted, then wanted to disable Firefox, to switch to Flatpak. Gives me error already.
I did not do anything yet…
rpm-ostree override remove firefox
Checking out tree 387ed50... done
Resolving dependencies... done
error: Could not depsolve transaction; 1 problem detected:
Problem: package firefox-langpacks-118.0.1-7.fc38.x86_64 from @System requires firefox = 118.0.1-7.fc38, but none of the providers can be installed
- conflicting requests
On a clean untouched Fedora 38 Silverblue, how is this possible?
Edit:
I had to do:
rpm-ostree override remove firefox-langpacks followed by rpm-ostree override remove firefox.
Perhaps because during Fedora SB setup i selected English UK instead of US? But I have nothing layered.
Edit2:
Since I have a clean untouched unlayered Fedora Silverblue 38 (with now only 2 packages removed: firefox-langpacks and firefox and RPMFusion repo added), I decided to try this command again:
rpm-ostree override remove libavcodec-free libavfilter-free libavutil-free libavformat-free libswscale-free libswresample-free libpostproc-free
Simply because I would prefer rpm layering, that way I can also easily use ffmpeg from terminal.
But this gives errors:
Checking out tree 387ed50... done
Resolving dependencies... done
error: Could not depsolve transaction; 2 problems detected:
Problem 1: package libchromaprint-1.5.1-8.fc38.x86_64 from @System requires libavcodec.so.60()(64bit), but none of the providers can be installed
- package libchromaprint-1.5.1-8.fc38.x86_64 from @System requires libavcodec.so.60(LIBAVCODEC_60)(64bit), but none of the providers can be installed
- conflicting requests
Problem 2: package gstreamer1-plugin-libav-1.22.5-1.fc38.x86_64 from @System requires libavfilter.so.9()(64bit), but none of the providers can be installed
- package gstreamer1-plugin-libav-1.22.5-1.fc38.x86_64 from @System requires libavfilter.so.9(LIBAVFILTER_9)(64bit), but none of the providers can be installed
- conflicting requests
Also libavcodec-freeworld and ffmpeg cannot be installed:
rpm-ostree install ffmpeg libavcodec-freeworld
Checking out tree 387ed50... done
Enabled rpm-md repositories: fedora-cisco-openh264 fedora-modular updates-modular updates fedora copr:copr.fedorainfracloud.org:phracek:PyCharm google-chrome rpmfusion-nonfree-nvidia-driver rpmfusion-nonfree-steam updates-archive
Importing rpm-md... done
rpm-md repo 'fedora-cisco-openh264' (cached); generated: 2023-03-14T10:56:46Z solvables: 4
rpm-md repo 'fedora-modular' (cached); generated: 2023-04-13T20:30:47Z solvables: 1082
rpm-md repo 'updates-modular' (cached); generated: 2023-09-16T00:25:03Z solvables: 1087
rpm-md repo 'updates' (cached); generated: 2023-10-10T01:24:48Z solvables: 25049
rpm-md repo 'fedora' (cached); generated: 2023-04-13T20:37:10Z solvables: 69222
rpm-md repo 'copr:copr.fedorainfracloud.org:phracek:PyCharm' (cached); generated: 2023-07-16T06:58:28Z solvables: 5
rpm-md repo 'google-chrome' (cached); generated: 2023-10-09T18:37:14Z solvables: 3
rpm-md repo 'rpmfusion-nonfree-nvidia-driver' (cached); generated: 2023-09-26T10:39:34Z solvables: 29
rpm-md repo 'rpmfusion-nonfree-steam' (cached); generated: 2023-08-10T16:27:32Z solvables: 2
rpm-md repo 'updates-archive' (cached); generated: 2023-10-10T02:42:32Z solvables: 41995
error: Packages not found: ffmpeg, libavcodec-freeworld
Using Flathub Firefox is definitely the only solution on a clean install.