The phrase "firmly concluding" is correct and usable in written English.
It can be used when you want to express a strong or definite conclusion about a matter.
Example: "After reviewing all the evidence, I am firmly concluding that the project will succeed."
Alternatives: "strongly concluding" or "decisively concluding".
The study firmly concludes that those coming now, and particularly those arriving from within the EU, are making an increasingly positive contribution to UK finances.
"Uganda firmly concludes that Kabaale-Tanga (Tanzania) route is the least cost route for the transportation of crude oil from the region to the east African coast".
"Reader, looke not on his Picture, but his Booke," Ben Jonson firmly concludes his dedicatory poem, right alongside the Droeshout engraving in the First Folio, and it seems the epitome of skeptical wisdom.
Given what Strauss' men have achieved over the last year or so, it would be wrong to firmly conclude about the result of this match with two days still to go.
In 1996, after having said earlier that Mr. Gigante might be competent to stand trial, Dr. Schwartz firmly concluded that he was, while two other psychiatrists persisted in their views that he was not.
This week a senior Bush administration official appeared to close the matter, saying F.B.I. and C.I.A. analysts had firmly concluded that no meeting had occurred, a conclusion first reported by Newsweek magazine.
The New York Times reported all too accurately that "a senior Bush administration official appeared to close the matter, saying F.B.I. and C.I.A. analysts had firmly concluded that no meeting had occurred".
We think it is too early to firmly conclude that it does.
They firmly concluded that propofol is a safe and effective drug to be used in PSA with no respiratory or cardiovascular depression, or other undesirable adverse effects.
Still, the review firmly concludes that today in fields where fewer women than men are obtaining faculty posts the reason is that fewer women are applying for the jobs.
