When you uninstall an Android app it will remove all the data from the device. There is no way for the app to warn the user that their data will be removed. It is unfortunate that your data is gone. If you used [https://support.mozilla.org/en-US/kb/sync-bookmarks-tabs-history-and-passwords-android Firefox Sync] then you can sign in and re-download your data. If you did not use this then your data is gone.