I once had a fantastic experience with reporting a bug on Firefox. One engineer saw that the bug was severe enough to justify delaying the release process, they

I once had a fantastic experience with reporting a bug on Firefox. One engineer saw that the bug was severe enough to justify delaying the release process, they worked their asses off to fix the bug and merged the bug into the new version which was released with just a little delay. That was amazing to watch. In general I have the feeling that Firefox and Chromium developers take bug reports very seriously. Safari is a different story, my bug reports there got frequently ignored. But I have the feeling that the entire Safari project is handled by one single developer, so it's not really surprising.