Latest Fire OS 5 user agents:

User Agent Browser Device
Mozilla/5.0 (Nintendo Switch; WebApplet) AppleWebKit/609.4 (KHTML, like Gecko) NF/6.0.2.20.5 NintendoBrowser/5.1.0.22023 Dalvik/2.1.0 (Linux; U; Android 5.1.1; AEOBC Build/LVY48f) NetFront Switch
Mozilla/5.0 (Linux; U; Android 5.1.1; KFSUWI Build/LVY48F; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/70.0.3538.110 Safari/537.36 OPR/32.0.2254.122938 Opera 32 Fire HD 10 (2017)
Mozilla/5.0 (Linux; U; Android 5.1.1; KFSUWI Build/LVY48F; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/70.0.3538.110 Safari/537.36 OPR/30.0.2254.121028 Opera 30 Fire HD 10 (2017)
Mozilla/5.0 (Linux; U; Android 5.1.1; KFSUWI Build/LVY48F; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/70.0.3538.110 Safari/537.36 OPR/30.0.2254.120995 Opera 30 Fire HD 10 (2017)
Mozilla/5.0 (Linux; U; Android 5.1.1; KFSUWI Build/LVY48F; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/70.0.3538.110 Safari/537.36 OPR/29.0.2254.120398 Opera 29 Fire HD 10 (2017)
Mozilla/5.0 (Linux; U; Android 5.1.1; KFSUWI Build/LVY48F; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/70.0.3538.110 Safari/537.36 OPR/29.0.2254.120012 Opera 29 Fire HD 10 (2017)
Mozilla/5.0 (Linux; U; Android 5.1.1; KFSUWI Build/LVY48F; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/70.0.3538.110 Safari/537.36 OPR/28.0.2254.119224 Opera 28 Fire HD 10 (2017)
Mozilla/5.0 (Linux; U; Android 5.1.1; KFSUWI Build/LVY48F; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/70.0.3538.110 Safari/537.36 OPR/28.0.2254.119213,gzip(gfe) Opera 28 Fire HD 10 (2017)
Mozilla/5.0 (Linux; U; Android 5.1.1; KFSUWI Build/LVY48F; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/70.0.3538.110 Safari/537.36 OPR/28.0.2254.119213 Opera 28 Fire HD 10 (2017)
Mozilla/5.0 (Linux; U; Android 5.1.1; KFSUWI Build/LVY48F; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/70.0.3538.110 Safari/537.36 OPR/28.0.2254.119114 Opera 28 Fire HD 10 (2017)
Mozilla/5.0 (Linux; U; Android 5.1.1; KFSUWI Build/LVY48F; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/70.0.3538.110 Safari/537.36 OPR/27.0.2254.118423 Opera 27 Fire HD 10 (2017)
Mozilla/5.0 (Linux; U; Android 5.1.1; KFASWI Build/LVY48F; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/59.0.3071.125 Safari/537.36 OPR/53.1.2254.55490 Opera 53 Fire HD 7
Mozilla/5.0 (Linux; U; Android 5.1.1; it-it; KFGIWI Build/LVY48F) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/59.0.3071.125 Safari/537.36 Hawk/QuickBrowser/2.4.4.22752 Hawk Quick Browser 2 Fire HD 8 (2016)
Mozilla/5.0 (Linux; U; Android 5.1.1; en-US; KFSUWI Build/LVY48F) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/57.0.2987.108 UCBrowser/12.11.3.1204 Mobile Safari/537.36 UC Browser 12 Fire HD 10 (2017)
Mozilla/5.0 (Linux; Android 5.1; KFTBWI Build/LMY47O) AppleWebKit/537.36 (KHTML, like Gecko) Silk/44.2.28 like Chrome/44.0.2403.128 Safari/537.36 Mobile Silk 44 Fire HD 10
Mozilla/5.0 (Linux; Android 5.1; KFMEWI) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.75 Safari/537.36 Chrome 86 Fire HD 8 (2015)
Mozilla/5.0 (Linux; Android 5.1; KFMEWI Build/LMY47O) AppleWebKit/537.36 (KHTML, like Gecko) Silk/44.1.54 like Chrome/44.0.2403.63 Safari/537.36 Mobile Silk 44 Fire HD 8 (2015)
Mozilla/5.0 (Linux; Android 5.1; KFFOWI Build/LMY47O) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/41.430.2250.2 Mobile Safari/537.36 cordova-amazon-fireos/3.4.0 AmazonWebAppPlatform/3.4.0;2.0 Chrome Webview 41 Fire 7"
Mozilla/5.0 (Linux; Android 5.1; KFFOWI Build/LMY47O) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/41.10.500.0153 Mobile Safari/537.36 cordova-amazon-fireos/3.4.0 AmazonWebAppPlatform/3.4.0;2.0 Chrome Webview 41 Fire 7"
Mozilla/5.0 (Linux; Android 5.1; KFFOWI Build/LMY47O) AppleWebKit/537.36 (KHTML, like Gecko) Silk/44.1.54 like Chrome/44.0.2403.63 Safari/537.36 Mobile Silk 44 Fire 7"