I don't spoof useragents with addons, I use general.useragent.override, and that's what I tried using to make the website identify me as Firefox 56. I do have some privacy extensions, but as far as I know, uMatrix and Privacy Settings don't change the useragent. Also, I'm not going to bother disabling everything to get like 40 or so more points on a test that I don't care for.
I'm running a not really up to date copy of 7, so the dlls might be a bit older, but they both have the version of 12.0.7601.23471 for me. I checked the ones in C:\Windows\System32