Last November he resigned as USWeb's chief executive officer and last month he stepped down as the company's chief strategist. The reasons for his departure have nothing to do with boardroom intrigue or corporate strategy. Rather, they have everything to do with little pointy-headed creatures from other galaxies. Firmage is now devoting his considerable energies - and even more considerable private fortune - to the proposition that cutting-edge physics will soon be able to prove the existence of UFOs and provide the technology to visit alien civilisations billions of light years away.
Freed from the day-to-day drudgery of negotiating corporate mergers and tracking USWeb's spiralling stock price, Firmage has set up a research body called the International Space Sciences Organisation, which will be based in a brand-new office suite in Palo Alto on the northern fringe of Silicon Valley. He is in the process of hiring 15 full-time researchers and has already published a 600-page tract on the Internet called The Truth (www.thewordistruth.org), outlining his various hypotheses.
"I am in a unique position to help raise the consciousness of the public at large, so they know there is something happening more important than what they are going to cook for dinner today," he explains. "This is about the storyline of the human race, a saga brighter than we can possibly imagine."
Is this also the storyline of a workaholic computer nerd whose frantic schedule and penchant for over-achievement has pushed him over the edge? A man whose ambitions, according to the introductory preamble to The Truth, have moved on from the mundane preoccupations of the dawning computer age to the more ethereal wish "to travel through the ocean of spacetime, to be among the stars of heaven"?
It's easy to be cynical, of course, and Firmage has been roundly derided as a wacko, a crackpot, a would-be visionary with an over-active imagination. Aside from his co- workers, who have praised his "courage" in giving up his executive positions, the only support he has received so far has been from the usual suspects - the reliable cabal of conspiracy theorists, modern-day shamans and prophets who are as addicted to this kind of stuff as they are incapable of putting their ideas into the mainstream.
The "giggle factor" goes with the territory, Firmage acknowledges, sitting in his old office at USWeb, in front of a desk piled high with merger and acquisition trophies, a mobile phone bleating forlornly in one corner of the room. But Firmage is also determined to prove his hypotheses in the only way he believes matters - on the basis of good science. "Someone of my credibility has not entered this space before," he says. "I will be able not only to provide funds for research, but also to track down the killer witnesses that can raise this issue out of the sewer of fantasy to which it has been relegated."
Science is where Firmage begins with the explanation of his theories, in particular the field of quantum vacuums and the hypothesis that the physical forces of the earth, such as gravitation and inertia, are governed by something called Zero Point Energy - a force which, if tapped, could extract enough power from a coffee cup "to boil the oceans of the earth".
"We know how to engineer electro-magnetism. So if it turns out that gravity is electro-magnetic it would be a fundamental revolution because one day we would be able to engineer gravity and use it to propel from world to world," Firmage says. "This opens up a whole field of seemingly anomalistic phenomena. UFOs are one; another is the power of consciousness to influence reality."
So far, so plausible. But as he pushes his hypothesis further, scientific conjecture gives way to very different talk, of an alien intelligence guiding humankind through history. "My contention is that science and spirituality are two sides of the same coin," he says. "This is not just about explaining the various sightings of UFOs since the Second World War. It's about the course of ancient human history.
"If you go back over a text like the Bible and insert modern words in place of the old ones - `aliens' instead of `angels', `space' instead of `heaven' - then a completely different interpretation opens up. It becomes clear that the human race is a young, new species granted occasional seminal lessons by teachers visiting this world."
At this point Firmage's gaunt, hollow eyes take on a special intensity and his forefingers reach up to clasp each side of the bridge of his nose. Religion is clearly a strong influence on Firmage's thinking. He was brought up in a large Mormon family in Utah, and - although he says he lost the faith of his forefathers as a teenager - takes care to list the Church of the Latter Day Saints in his acknowledgments for The Truth. If his career took such an unexpected turn to the left, it was not just because of his dabblings in the latest academic physics journals. It was also because, like St Paul on the road to Damascus, his life was turned upside down by a transfigurative revelation.
As Firmage himself tells it, he was lying in bed early one morning in October 1997 and had just hit the snooze button on his alarm clock when this happened: "A remarkable being, clothed in brilliant white light, appeared hovering over my bed in my room. He had dark hair and a beard, I believe. He looked rather annoyed, and asked, `Why have you called me here?' I answered without a moment's pause: `I want to travel in space.' This was always my lifelong dream, and it naturally came out in a state of semi-waking thought.
"He chuckled sceptically, paused, and asked, `Why should you be granted such an opportunity?' I responded without hesitation, `Because I'm willing to die for it!' The visitor was visibly shaken. He stepped back. He stared at me, lowered his head, and out of him emerged an electric blue sphere, just smaller than a basketball, which was swirling with what looked like electrical arcs. It left his body, floated down, and entered me. Instantly I was overcome by the most unimaginable ecstasy I have ever experienced - a pleasure vastly beyond orgasm. My body shook as I awoke, and continued to shake for what appeared to be minutes. Something had been given to me."
That something, according to Firmage, was the realisation that he had to take his life in a totally new direction: "It was so overwhelmingly obvious that something grand was in play that I could not stay silent any longer." So he contacted a group of scientists working on Zero Point Energy, read up everything he could find in the UFO literature, and began to formulate a general theory of human existence - a theory that has now taken the form of his Internet book but is, he says, constantly evolving.
It is the second of The Truth's four parts that has attracted most attention, because it dwells on the old theory that an alien spacecraft crashed near Roswell in the New Mexico desert in 1947, and that the US government has since striven to keep the episode top secret for fear of unleashing a universal wave of panic. The web pages of The Truth entertain many variants on this theory from several different authors - that modern technology, including the development of computers, has borrowed generously from the findings at Roswell; that contact with aliens is what led President Truman's naval secretary to go insane and kill himself; that the secrets of Roswell are now in the hands of a self-appointing private committee of around 1,000 industrialists and ex-military officers.
"Consider that within six months of the Roswell incident, Truman passed the National Security Act, the CIA was formed and the Air Force split from the Army," says Firmage. "We have documents whose authenticity we are doing our best to prove showing that Presidents Truman, Eisenhower and Kennedy all participated actively in investigating the UFO phenomenon. Look, 80 per cent of what has been written about UFOs is total garbage, but the other 20 per cent is based on serious research."
Sure enough, among the items put out on the Internet are the so-called Majestic Documents - apparently confidential government correspondence from 1947 to 1963. Here we have Robert Oppenheimer, father of the atom bomb, discussing extraterrestrial life in a memo to the President, directives from Harry Truman ordering senior military personnel to investigate the Roswell incident and detailed reports sent back to him.
The last two items in the batch purport to be memos from President Kennedy, the first requesting a review of "MJ-12 Intelligence Operations" - possibly a reference to the secret UFO committee - from the director of the CIA, and the second proposing a joint space exploration programme with the Soviet Union in connection with "UFO intelligence". The second memo is dated November 12, 1963, 10 days before Kennedy's assassination. Could there possibly - now we are in full conspiratorial mode - be a link between the alien visitors and the most mysterious political crime of the 20th century? Firmage winces visibly at this suggestion, realising that even he isn't easily going to be able to explain away a theory as explosive as that.
"That's the last thing I need to be associated with right now," he confides, and at the corners of his impeccably earnest face there is the faintest trace of an incipient smile