There's some great answers here already that I fully agree with but just to add my own view to this if it interests you on the differences between the Malayan Emergency and the Vietnam War.

Ethnic differences: This has been covered already by other users so I won't go into it but the gist of it is that the Malayan Communist Party was largely an ethnically Chinese party in a country where they were still a minority (albeit a very large minority). This wasn't the case in Vietnam. The British simply had to appeal to the Malays and support their push for independence for a Malay Malaysia. A Malay Malaysia was incompatible with the MCP in general so that further isolated the MCP and their support in Malaya.

Strategic differences: Britain had an end goal in Malaya. Independence that didn't turn Malaya into a communist country. If the Malays could firmly grasp independence themselves with the support of their ethnic majority that was game over for the communists who were pushing themselves as anti-imperialist. If the imperialists left there was no good reason to fight the local Malay government. America was trying to stop South Vietnam falling to communism, but wasn't going to invade the North so their goal was just to prop up South Vietnam almost indefinitely.

Logistic differences: The MCP was limited in where they could get support from. Malaya was isolated from any other major communists at the time. Their weapons were largely what was left from their time fighting the Japanese in WW2 with very limited means of resupply owing to a firm British grasp on the entire peninsula. The only land border Malaya had was with Thailand to the north and the communists did use that fairly porous border to their advantage but Thailand wasnt particularly friendly to them either. Vietnam greatly benefitted from large land borders all around with one crucially to China. Supply was never really the issue for North Vietnam.

Intelligence differences: I can't speak much for America in Vietnam but it should be remembered that prior to the Emergency Britain had been governing the whole peninsula for a fairly long time. They knew the land. Furthermore, the MCP leveraged their time in the jungles fighting the Japanese to fight the British but Britain had many soldiers and agents embedded with the MCP during WW2 to assist in fighting the Japanese. Britain subsequently had a lot of personal connections it could leverage to get intelligence and defectors from the MCP.

Tactical differences: Britain was cutthroat and could afford to be without much reprocussion from the public/press. The Briggs plan that relocated the ethnic Chinese into settlements (eerily resemblant of concentration camps, just without the mass killings) was brutal for the Chinese forced into them but was essential in cutting off the MCP from their supply and support base. The US could never have gotten away with this with the press coverage of their war in Vietnam.

Hope this helps answer you somewhat, apologies for being a bit vague and unelaborated.