> The “Backspace” keyboard shortcut on Firefox is by far the keyboard shortcut with highest usage with 40M MAU, well above “Find in page” (16M MAU) or “Page reload” (15M MAU), causing concerns that our users suffer useability issues and data loss issues from hitting this keyboard shortcut by mistake
I'm surprised they didn't get the statistics for how many people went forward within 1-5 seconds of a Backspace press to undo it.
It seems they saw that the ratio using Alt+Left (2M) and Alt+Right (0.5M) was different to Backspace (40M) and Shift+Backspace (0.3M). However it makes sense a single key shortcut is more discoverable. The first time it's hit might be a mistake, but the following times might be on purpose.
It's likely the Firefox developers use more of its shortcuts because they are more familiar with the product and are more interested in optimizing their workflow than a typical user. Exploring, which includes backtracking, is the core of the web browsing experience so I'm not surprised people are doing that far more than, say, searching for a substring.
It's also worth pointing out there isn't a great opportunity to learn the keyboard shortcuts Firefox provides. Traditionally you'd learn shortcuts by seeing them next to menu items, but the menus are hidden behind the Alt key, and many actions simply aren't listed there. For example, "Find Again" / F3 is omitted.
I'd assume that there is a class of users who never ever use any keyboard short deliberately (because they are not aware or dont care about their existence). Any keyboard shortcut they trigger is pretty much by accident. I have not data how common that is, but I know such users.
That seems to just be majority of users based on that stats listed above, and that backspace is the only one that is trivial to hit when trying to do something else.