Argh this kind of thing makes me really cross. So many sites seem to feel the need to reimplement things that are already part of most browsers or even in the spec. It's not just overridng default shortcuts, but custom context/rightclick menus, custom 'links' (where clicking them runs javascript code to window.open, instead of being a real link), custom form fields that advertise 'excellent accessibility', where the fields would have been accessible anyway if they didn't decide to reimplement them, disabling text selection, overriding focus styles because the accessible styles 'look ugly' ... the 'modern' web is pain.
Anyway, this wasn't going to be a rant. My point was going to be that consistency is key. Your comment on '"Ctrl+F" instead as I'm too scared to try "/" now' really resonated with me, because I've thought about this before. I've found that a feature or shortcut is only useful if it's consistent. I can't build muscle memory or be confident using a feature if it only works 90% of the time. Or even 99%.
I've tried tridacyl and other vim-style plugins for browsers several times in the past, but always end up uninstalling them in disappointment, because it's not possible to have a consistent experience. 99% of the time it works perfectly, but then there are the handful of sites or browser specific pages (eg. about: or view-source:) where it doesn't work at all, or doesn't work consistently so one must disable it. Then muscle memory totally breaks; you need to learn two sets of keybindings for the same context, and that introduces a hesitation for every keypress, which kills speed and enjoyment.
The more consistent something is, the less you have to remember. But it can be really hard to do things consistently for various reasons.