I typically use Ctrl+# to switch between tabs, but while making a post just barely, I noticed that doing so changed the formatting of the line I was typing. I'd then Ctrl-Z to get the formatting back, but the last update for undo was the sentence I'd just typed, so I'd have to retype it. This got quite annoying by the time I finally started moving my hand back over to the mouse to switch tabs.
I think this really ought not to be the case. In-browser apps have certain shortcuts they're not supposed to mess with (unless it's something really complicated like Google docs, where it's practically its own program). I don't think very many people would miss the ability to use shortcuts to make headings, and it would immensely help those, like me, who need to switch back and forth between tabs often.