After watching this replay, I definitely think the firefly is OPed. But I disagree that the brits are OP in general, as the emplacements you did build got handly beaten by a player who executed wehrmacht almost to perfection.
I thought this game was an excellent example of how to play wehr vs. brits, except for the OPed firefly.
nervme had the right stat by going speed t3 vs. brits, who have jack all to counter it until they get fireflies but instead of driving around the at gun, he seemed insistant on a frontal assault. He ignored the VPs and let himself get bogged down at t3 while fireflies came out. If he'd have just assaulted earlier, if he'd have had a few volks out there capping, if he'd spare a few stugs (which are junk anyway) to go t4, he'd have this match.
Brits are NOT OP. They are tough early game, but merely annoying late game because they don't have any real tanks. Fireflies are better than stugs, but then everything is better than stugs.
I'm finding the best thing to do is find the armor truck and annihilate it before he gets too many fireflies out. Just keep artying the British entrenchments in the meantime maybe, use storms. I do think Brits are a little OP on maps like Wrecked Train where it's easy to set up a nice defensive line that's pretty hard to flank without going through so much crappy jumbled landscape, past buildings, etc. But as long as you can flank the little tea-drinking wussies, you can win.
Too many no vet volks too at the start. I just go Mg/bike/sniper/volks maybe another mg if they seem to want to run around. Bike chases the LT around, mg suppresses, sniper soots at the second infantry squad that can't snipe back. Volks are pointless against Brits, unless they have vet and MP40s. It's like rifles dying to Fallshrimps, only slower and somehow more pathetic to watch.
Just so you know, when an enemy sniper shoots at your marksmen squad, then disappears, as long as you told it to deploy marksmen on the sniper, if the sniper re-appears within before 10~ seconds, the marksmen squad will shoot at the sniper. I watched SO many times as you stood there and let your marksmen squad eat sniper bullets. Make sure you deploy marksmen!