This problem is on your Android phone? Then I would start by turning off the phone completely. Pull the battery if possible. Then go into your Google account on a regular computer and change your password. Hopefully this will limit the damage that someone with control of your phone can do. Since this question isn't about Firefox, I think you could get a more comprehensive solution from Google support or from an Android forum. * Gmail support forum: https://productforums.google.com/forum/#!forum/gmail * Android user forum: http://forums.androidcentral.com/