We really aren't trying to make anything annoying for you. We're trying to keep the site running for everyone. And yeah, there are a bunch of little things that just aren't things we can solve because behaviors like that are controlled by your browser. I've not had my cursor disappear, but I also don't post nearly as much as any of you. I've had ads change/pop up when I'm typing and didn't notice any loss of focus on the typing box. I'm not saying it's not happening to you, but there are a LOT of reasons it can be happening, and it might even be an ad (we sometimes get ads doing stuff we don't like and have to go exclude them once we notice.)
Now, if we can see a bug and reproduce it, that's much easier to track down and try to fix. And we've been pretty good at keeping the serious bugs at bay.