They were strongly against it.
Well I feel strongly about getting my nails long. I was a biter but now I have white showing and hopefully I will have them longer!!
It depends on the context. "Feel more strongly" could be used in regards to an opinion, such as "I feel more strongly about world peace than I do about celebrity banter". "Feel stronger" is associated with your sense of physical strength, i.e. "I feel stronger after going to the gym for six months than I did prior".
segregation
She hated Ares strongly.
Very.
Strongly opposed.
there was another continent out there.
Very strongly
Of course when someones depressed they feel feelings very strongly
strongly about
Amelia felt very strongly about women's rights and their ability to do the same jobs as men.