…at least from a system administrator point of view.
Firstly, although it appears by default to be configured to ‘Use system proxy’, it ignores the system proxy settings – unless it simply takes the actual proxy settings, and nothing else.
The Windows system proxy in my network is set to ‘Configure automatically’, because I have DNS wpad configured, which firefox does not appear to use. You have to configure the proxy.pac manually.
Secondly, it ignores the Windows certificate store. It has its own certificate store, which means I have to manually import the root CA certificate I want it to trust. Fortunately in my case, I only have to worry about my kid’s computer. If I had to do this in an enterprise situation, it would be easier to simply ban the use of Firefox in favour of chrome. Personally, I prefer to use Chrome at the moment.