"I used to spend three and a half hours every day on the London Underground. I was absolutely exhausted. It finally wore me down to the point where I had to move. I have loved working in Stratford but doing a 10-hour day can wear you down."
Last month Mr Firmin took up his new post as vice-principal (resources) at one of the country's oldest adult education colleges, The Working Men's College in Camden, north London.
He has spent the past seven and a half years helping to turn round Stratford School, one of the first grant-maintained schools in the country. When he arrived, the school's finances were in a mess, its academic results were terrible and Newham council wanted to close it. The local Muslim community was keen to turn it into a Muslim-only school and scarcely a day passed without its featuring in the media.
Today the 11-16 mixed-sex, two-site comprehensive - a foundation school with more than 900 pupils and fully refurbished premises - is thriving. Mr Firmin, whose previous jobs include working as an accountant at Thames Valley University nd at Ealing College, says his new role will be quite a challenge despite the relative smallness of the institution. The college, he adds, has a terrific tradition.
Founded in 1854 to provide a liberal arts education for the Victorian skilled artisan class, it is closely associated with the Co-operative movement and stems from the same tradition as the Workers' Educational Association.
Early supporters included F D Maurice, the founding Christian Socialist, professor and priest, the first principal, Tom Hughes, the author of 'Tom Brown's Schooldays', Charles Kingsley, the clergyman, reformer and novelist most famous for 'The Water Babies', Dante Gabriel Rossetti, the Romantic poet and painter, and John Ruskin, writer on art and society.
Later volunteer teachers have included G M Trevelyan, Liberal historian, E M Forster, novelist. C E M Joad, author and philosopher, and Seamus Heaney, the poet.
In 1967 it merged with its sister college for Working Women. Until recently the volunteer tradition prevailed in the teaching and management of the college. Sixty per cent of its curriculum is offered via evening classes.
In his spare time, Mr Firmin, who is married with two children, plays football, cricket and squash and drums in a blues band.