'firmly feel' is correct and usable in written English.
You can use it when you want to emphasize the strength of your feeling or opinion about something. For example: "I firmly feel that honesty is the best policy."
He firmly felt — and still feels — that the prosecutor had not proven every element of the charge, but the adult monitor riding the bus turned out to be his neighbor across the street in Ardsley, and she snubbed him for months.
Time – Shakespeare's choric voice – is a strong presence in this version, but perhaps she should have made her presence more firmly felt: the timing is a little unbalanced, a casualty perhaps of reversing the order of the first four acts, rather than beginning with the depiction of Leontes' jealousy.
Moreover, there is evidence to suggest that intuitions supporting some version of the psychological criterion are not only firmly felt, but quite common (Nichols and Bruno 2010).
Last summer the European Union's Competition Commission made its presence more firmly felt by slapping Google with a record breaking $2.7BN antitrust fine relating to the Google Shopping search comparison service and following a multi years investigation.
Therefore, despite the persistent and resurgent racism in the U.S., I have always, proudly and firmly, felt very American.
"It firmly felt like the kind of call you make when you're trying to feel out if someone has the interest and/or standing to bring a lawsuit," said Salsbury.
"They want to send an unequivocal message about how firmly they feel about the situation in Tibetan areas".
I admire how firmly you feel about all art being subjective.
Our 2015 forecasts feel firmly underpinned with risk already on the upside.
