'firmly founded' is correct and usable in written English.
You can use it to describe a foundation or belief that is secure and well-established. For example, "Their relationship was firmly founded on trust and respect."
The 33 quartets from Opus 50 onward (excepting Opus 51, The Seven Last Words) include the masterworks on which Haydn's reputation is so firmly founded.
Now that I have put my work in it's place, I would then assert that the animations are firmly founded on real data and are as accurate as I can possibly make them, while making them watchable and interpretable to a human audience.
As a result, the National Review's list of movies is much more firmly founded than their Rock Music list was, because the industry needs to tease out the endorphins of everyone from time to time in order to pay the bills.
"There must be more equality established in society, or morality will never gain ground, and this virtuous equality will not rest firmly even when founded on a rock, if one half of mankind are chained to its bottom by fate, for they will be continually undermining it through ignorance or pride".
Telepathy is a design firm that was founded in 2001 in San Diego and ServiceNow decided to purchase a company firmly focused on design because it wants to nothing less than transform itself into a design-oriented company.
But I firmly believe that national policy founded on too myopic principles merely extends problems for this country.
More recently, Steve Jobs, who founded Apple Computer, has established himself firmly in the industry with Pixar Animation Studios.
The Athens Symphony Orchestra was founded in 1978 as a firmly non-profit, strictly volunteer organization, conducted by Albert Ligotti of the University of Georgia.
The group Ms. Blander founded, the New York Cosplayer Network, falls firmly in the latter category.
By 825 they had firmly established themselves in southern and southeastern Myanmar and founded the cities of Pegu and Thaton.
Fether said: "Since they founded Bwark seven years ago, Iain and Damon have firmly established their position as two of the UK's most talented comedy writers and producers.
