To follow up on (https://addons.mozilla.org/en-US/firefox/addon/keepassxc-browser/reviews/1279287/)
I also feel this extension has little to no use (especially for Firefox) First of all. the auto type sequence is a highly dangerous function. Even if the record inside the keepass database is all set to work for multi page logon, and one changes the global settings by accident. (or update!) all the custom fields are vanished Thus text is just injected into space.
And this is just a KeepassXC bug/~feature~
*sidenote: On Chromium on ubuntu the extension just works out of the box.
On firefox 10 out 10 times this extension is not connected to the database and even if the extension believes to be connected its not, due to KeepassXC not getting kicked alive.

For these hasles it it just not worth the effort.
Just learn the keyboard shortcuts to quickly find and copy the fields needed and insert them manually. The proxy to tunnel the uname/pwd into the browser will not be available i assume.
Second to that: I believe that if your pc is already in a state where you can't trust your computers (basic) functions as per example the clipboard; one has a whole lot of other problems to deal with prior to thinking about security and privacy enhancements
endnote: 5 (Five) stars for the time and effort from the team on KeepassXC itself