It has nothing to do with website design. It's part of the HTTP protocol. A poor part in today's understanding and use cases, but in the 90s it would have made sense.

FAA is one of the better government agencies. In the US, they'd have to be tested and be shown to work on a regular basis in the same way that the emergency rafts and oxygen candles are tested.

It's worth noting that all commercial aircraft that operate over water (so, the vast majority, excepting very small commercial aircraft and four-engine behemoths) have ETOPS ratings. [ETOPS, Extended-range Twin-engine Operations Performance Standards](https://en.wikipedia.org/wiki/ETOPS#:~:text=ETOPS%20(%2Fi%CB%90%CB%88t%C9%92,%2Dengine%2Dinoperative%20flight%20conditions.) specifies the amount of time the aircraft can operate on a single engine, measured in minutes. ETOPS-180 is a pretty common rating.

But why? There's no need for a PDF editor in a browser. This is just raising the size and lowering the performance of a browser for a feature that almost no one needs or wants.

Mozilla should probably build a PDF viewer/editor (Adobe sucks and Foxit has gone downhill in recent years), but it's not part of Firefox.