What is the problem?

Andrew! Sorry that was unclear. I have no idea how this topic missed Title and I was not able to edit later to add a clear Title to convey my concern. If possible, please suggest Firefox team to use 'Discourse' software for forum. It would make life easier. Exact issue: If you check my screenshot & video you will find there is a gap of 1px between address bar & my sticky navigation. You may notice background element such as color/font will appear (depending on page element) I was able to repro this issue at https://policies.google.com/privacy?hl=en-US in Firefox Android 79.0.5 Build #2015758619 version as well. I don't see this same problem while using other browser (Chrome). So, this is likely something with FF. If this is unclear, please do let me know. I'll send more details.