Hi I am sorry to hear that this is happening. I do not think this is an issue with Firefox for Android, but may be due to either a) someone obtaining your master Android account credentials and/or b) malware being present on your device. This [https://www.kaspersky.co.uk/resource-center/threats/mobile article] gives details of the different types of mobile malware you should watch out for. To help secure your device, I recommend changing your master gmail account password and reviewing the applications you have installed on your device. Whilst Firefox for Android is an app you can trust, you may have inadvertently downloaded a harmful application or two that you should remove.