App has been uninstalled and reinstalled too. Tried without sync or logging in with my Firefox account, same issue.

Hi I am sorry to hear that Firefox for iOS is crashing. I hope that we can help resolve this for you. Before following the steps below, please make sure that you have updated both your iOS device and Firefox for iOS to the latest versions available. As a first step, close down many of the tabs that you have open to as few as possible. Does this help reduce the incidence of a crash? If this does not resolve the issue, open the iOS Settings app, select General then iPhone Storage. Find Firefox and select Offload App. Does this help? Failing that, we will need to look into this in more detail with some logs from inside your copy of Firefox for iOS. This [https://github.com/mozilla-mobile/firefox-ios/wiki/How-to-get-your-device-logs article] will walk you through getting both crash logs and Firefox logs. When you have them, please file them [https://github.com/mozilla-mobile/firefox-ios/issues/new?assignees=&labels=Crash&template=---crash-report.md here] (a GitHub account is required) so that our developers can look into this further for you. I hope that this helps.