if u consult wikipedia, if it really is 1st gen kindle fire , that's a 2011 device running amazon's fork of android 2.3.3. ( amazon version 6.3.4.)
the changes of finding any app , nowadays, that is android 2 compatible is ,er, lets say remote ( to be polite)
chances improve if its a 2012 2nd gen, as that's android 4. still going to be a poor experience though
https://en.wikipedia.org/wiki/Amazon_Fire_tablet#Models
the same google search tells me that ebay has several 1st gen kindle fires for sale, for the gullible