You have to download the favicon for every single entry.
Having a huge database without any custom icons set, this new feature would dramatically reduce manual effort.
_Update 2017/10/05:_ It might also be useful to add an option to force an update of existing favicons.
Yeah this feature would be really awesome (after they get around fixing the favicon fetching)
@kusaha what is the problem with favicon fetching?
@TheZ3ro
When you try to get favicon from "https://*" URLs keepassxc always fails to fetch them, showing this error:

but there's already an open issue about this here: #678
(Note: I'm using windows 10, and the 64bit version of keepassxc)
@Kusaha, possible workaround is to use Favicon downloader plugin with original Keepass.
Just in case anyone else is having the same troubles I am...
For whatever reason I couldn't get the SourceForge mirrors to let me download the original Favicon downloader plugin for KeePass, so I'm using this plugin instead, which seems to work so far: https://github.com/navossoc/KeePass-Yet-Another-Favicon-Downloader
Looking forward to seeing this as a feature for KeePassXC so I can finally throw my old KeePass install away.
I'm using KeePassXC 2.3.4 and I can't find this "favicon download" option. Where is this?
You need to define a url for the entry. Then go to the icon section on the left of the edit entry page. The button is at the bottom.
An "Update all favicons" would also be useful. For first time downloading all favicons and for downloading and setting new favicons over old ones if there are any.
I opened a work-in-progress PR that you can try: https://github.com/keepassxreboot/keepassxc/pull/3169.
Most helpful comment
Just in case anyone else is having the same troubles I am...
For whatever reason I couldn't get the SourceForge mirrors to let me download the original Favicon downloader plugin for KeePass, so I'm using this plugin instead, which seems to work so far: https://github.com/navossoc/KeePass-Yet-Another-Favicon-Downloader
Looking forward to seeing this as a feature for KeePassXC so I can finally throw my old KeePass install away.