On firefox if you use the sidepanel with bitwarden it is unusable in all the acceptable sizes.
Bitwarden requires a greater horizontal space in the side panel, where as other applications are capable of working in the minimum size requirements of the panel.
The options provided by bitwarden are as such (“default”, “wide”, “extra wide”). It is unreasonable for a sidebar application to require such a large size. Here I have my bitwarden account on the minimum size where I can see everything. Notice how it takes up almost half of the screen.
I would request that bitwarden either alter their design to work with the minimum size in firefox, or that by hover over the web icon in the left gives you the option to fill, copy username, and copy password. This way the system is still mostly usable in a compact form.
