I have covered this issue on [https://support.mozilla.org/en-US/questions/1310000#answer-1360860 https://support.mozilla.org/en-US/questions/1310000#answer-1360860]: <blockquote>The tablet uses an Android-based system, which does not have built-in Google services, and thus no ''Google Play Store''. If you want to easily download Android apps, use '''[https://www.howtogeek.com/232726/how-to-install-the-google-play-store-on-your-amazon-fire-tablet/ this guide]''' to install the ''Google Account Manager'', ''Google Services Framework'', ''Google Play Services'' and ''Google Play Store'' on the tablet, all of which are necessary for the Play Store to function. (Basically, you download a few ''.apk'' files - basically Android '''''a'''pplication '''p'''ac'''k'''ages'' that can be extracted and run by tapping them in your file explorer (may be known as ''Documents'' on Kindle Fire). This is usually done in the background by the app store but you can do so manually if you allow ''installing apps from unknown sources'' is ''Settings→Security''.) This option is preferred if you already have a Google account and want to easily download most Android apps, though the ''Google Play Store'' and related services will take up some storage (you can uninstall them but updates for your apps will no longer be taken care of). If you are low on storage, don't want a Google account, do not care about other apps or want to select an older version of Firefox, download Firefox's APK only (e. g. [https://firefox.en.uptodown.com/android/download from uptodown.com], [https://www.virustotal.com/gui/file/84fa89a5160d16a179bcfa6405b326f9aa28437a41b8a23a7a467476e379426b/detection checked with VirusTotal]) and use this guide to install it; it is quite straightforward. You can use this process for any Android app, but beware that unverified APKs may contain viruses or be other unwanted software, and some functions may not work without ''Google Play Services''. Reply if you need any more help. </blockquote>