With respect to functionality the add-on works generally very well. Unfortunately, even with newest versions of Firefox, listing open port connections still shows several open connections from the keepassxc-proxy add-on to sites like googleusercontent.com, cloudfront.net, amazonaws.com and akamaitechnologies.com. Developers claim that this is a bug in Firefox beyond their control, however, the open ports are reported specifically for the keepassxc-proxy process, not for the parent firefox process. This behaviour is not particularly trust inducing.

very useful extension, works perfectly on every Operating System allowing a smooth browsing keeping safe my passwords

unfortunately, it doesn't works on Firefox snap version (nowadays snap is default on Ubuntu)

Works great on most websites, but really struggles on others. I can't get it to work at all on Twitter, Reddit or iCloud.

Not as smooth as expected. connection to application is not opened sometimes and had to click on icon to establish it. "your password has changed" prompt comes even if it has not been changed. also saving new password is a miss more times that it is a hit. you just have to hope that banner will appear. Most of time I manually go and add the password as a entry.

Doesn't work in Ubuntu 21.10 out-of-the-box. You have to uninstall the default snap version of firefox and then install the host version. Would be nice if this was in the documentation.

Definitely a little buggy, unlike the main app. Once had an issue where the banner for updating an entry showed up despite the credentials not differing, the banner failed to appear on the next page despite being set to appear after infinite redirects, then on my next login on a different website I was notified that my database had changed despite me not interacting with the banner or database, I said to discard changes, after which the main app froze. Restarting the app usually fixes things, and when the extension works it works well.

Works only for a part of sites. For all others just can't fill in credentials. Also when creating a new account a pop-up bar displayed to store new data. But click in it produces error "can't save credentials". Meanwhile the database is connected and unlocked.
So I decide the plugin to be quite buggy.

Would love official support for Waterfox on Windows. Unfortunately the Custom Browser feature seems to be MacOS and Linux only for now.

Виснут некоторые сайты из-за этого дполнения. Не всегда находит пароли

For the most part, this functions ok and I'm able to use it. Unfortunately, for some sites (such as https://cards.barclaycardus.com/) it just doesn't seem to detect the un/pw fields even after I manually select them. Barclay's site is particularly strange. When I "choose custom login fields" I get two of the "overlays" for choosing fields. I have issues on Community America Credit Union's site as well, which might have something to do with the fact that the login form "pops open" when you click in the username field. I haven't really had any issues connecting to my KP database, mostly just issues with the auto-fill/field detection. Thanks for the all the hard work though, I appreciate it. I'm sure over time these kinks will get ironed out.
EDIT: PopOS! 18.04 (so ubuntu 18.04) & Firefox 69.0.1

Nice extension but it may take some time to understand how it works and some sites become extremelly slow because of it, in my case it is Jenkins (configuration pages, plugins page).
Also, it lacks some features:
- save extra fields, like account name/number, etc (e.g. AWS)
- it does not populate login and password on some sites, although it can save them (e.g. Sonatype Nexus)

Shortcuts don't work :(

Pratique, mais pas très intuitif : l'intégration est minimale et il faut repasser par KeePassXC régulièrement.

Gros problème de gestion de l'obsolescence : depuis plusieurs jours, le plugin n'est plus utilisable car il demande la toute dernière version mineure 2.4.* alors que le gestionnaire de paquet de ma distribution (pacman) propose toujours la 2.3.4 et seul une beta de la 2.4 est dispo sur AUR.
Une rétrocompatibilité aurait été bienvenue, même temporaire, afin d'assurer un suivis pour les utilisateurs moyens qui ne vont pas chercher à compiler les source depuis un GIT et se reposent majoritairement sur leur gestionnaire de paquets.

Spent a lot of my time just trying to get it to work. Finally I've done it but I'm an IT technician and I believe that most of regular people will fail here.
And according to the feedbacks it seems there is a lot of such failed tryouts when people can't even start to use it. Please do something with that.
For example my case was that:
1. Different versions (64-bit FireFox against x86 KeePassXC portable). Extension runs proxy but nothing happens futher - extension doesn't see proxy running or something like that. Fail.
2. KeePassXC (installed) doesn't make org.keepassxc.keepassxc_browser_firefox.json nor apropriate registry entry - proxy doesn't run. I believe that's because of UAC and permissions. Still hothing works. Fail again.
3. Portable x64 KeePassXC + Firefox x64 - win. It creates json and write proper registry key. Extension runs proxy and they both interact each other.

Useful but lacks proper documentation. I could only find documentation pertaining to installation and configuration, not to actual usage.

Was really looking forward to trying this out, but I can't seem to get it to work at all.

Tested with FF 64.0 Portable, KP XC 2.3.4 Portable, and followed directions at https://keepassxc.org/docs/keepassxc-browser-migration/ , but cannot seem to get the browser to connect to the DB. Per the instructions, I've enabled browser integration for FF, but receive the following Error from the plug-in: "Cannot encrypt message or public key not found. Is native messaging or support for your browser enabled in KeePassXC?". Reload button doesn't help, nor does restarting the apps.

EDIT:
Thanks for responding. It sounds as if I need to make some changes to the FF launcher's ini file (in order to get FF Portable to work with this), but it's unclear what those changes are. After searching around a bit more, I see that others are experiencing this problem as well:
https://portableapps.com/node/57907
https://github.com/keepassxreboot/keepassxc/issues/1817

I saw some information at https://github.com/keepassxreboot/keepassxc/issues/1559#issuecomment-369508900 regarding what registry entries need to be shared, but it's unclear to me exactly what steps I need to take to get FF Portable to work with KeePass-XC portable. Could you provide a bit more information about exactly what .ini files I need to edit and with what changes?

EDIT 2: Another user commented that disabling the proxy (Tools > Settings > Browser integration > Advanced) solved the integration issues. I've tried this, and it seems to be a good workaround. The downside is that a second copy of KeePass XC launches with the proxy disabled, but at least it seems to work.

While the program works very well, the extension does not. Website detection is hit or miss, and there is a fill TOTP button that does absolutely nothing.

UPD. Please make this addon auto update connection to database, when press to icon

Works most of the time but can struggle to detect credential fields, doesn't seem to redetect them after re-connecting to the database.

Creating new entries does not work in the latest version (no blinking icon at all). It requires 2 clicks in version 1.13, but at least it works.

Previously was perfect, but perhaps the latest upgrade of Firefox 60.0.2 64 bit has broken it as it now doesnt fill fields since upgrade FF a couple of days ago.