UPD: works as intended. Issue that was described here is gone.

Sometimes it's doesn't work, I must reinstall addon and it's work again.

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

The best one right now.

Not working in 99% of the time. You have to delete and and create database connection every single day because your current connection "Cannot decrypt message" or smth else.

Both the tool as well as the plugin works OOTB with Firefox 64 (Linux Mint/Ubuntu Bionic). Good work, I like it.

With Ubuntu 18.04 and latest Firefox it is unreliable, in 2/3 of the cases I get a Timeout and in 1/3 of the cases I'm able to connect. I couldn't find any reason why it works or why It doesn't work. I tried on two different machines. I couldn't find a way that reliably gets a connection. And I do have apparmor working. Trying it was a waste of time.

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.

with KeepasXC 2.3.4 (only this version) plug-in works as intended.
The only things missing now are:
- Ability to unlock database in the background (i.e. without opening KeePassXC
- Automatically re-scan login forms to detect / identify login fields.

== my original 1* review ==
Does not work. Every time I close my browser, I have to go though "connect" process.
Even if it did work - one has to manually open KeePassXC application and unlock database (which means, navigating away from the browser). If I'm opening KeePassXC anyway, why not copy/paste password from the application then, why use some plugin?

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.

Does not work reliable. Need to be more stable. (Firefox-Version)

Problem: The key between the KeePassXC-Browser Add-On and the KeepasXC database (stored in the root folder) to exchange the secret data is not the same. (key: the secret key the exchange data bewteen the add-on, proxy (optional) and KeePassXC database. I compare the first digits)

This issue leads to that point, that every time the user closes Firefox and start Firefox later (say: next day or so) he has to regenerate all the connection information and login with a new name. The connection is not persistent. It's like every time before you close firefox you remove the connection info from the KeePassXC-Browser Add-On.

Same happen if i enable or disable the "Use a Proxy application bewteen KeePassXS and brwoser extension" in the advanced settings tab from KeePass. So, i think, it is not a issue of the proxy.

System: Ubuntu 18.04 LTS, Firefox 63.0, KeePassXC 2.3.1, KeePassXC-Browser Version: 1.3.0

Same happens under Ubuntu 16.04 LTS with a manuall KeePassXC Installation - because KeePassXC is not part of the regular Ubunut 16.04 distribution.

This seldom works. I've spent over an hour (not an exaggeration) trying to get KeePassXC-Browser to store credentials for websites I frequent. It connects to KeepPassXC but cannot detect login fields even if you explicitly point them out to the extension. I might as well use KeePassXC as a standalone and constantly put my credentials on the clipboard.