The goal is to make it easier for users to perform a site-wide "find".
You can easily disable it by using the checkbox on the bottom right of the overlay that appears; then cmd+f will behave similar to your browser's setup.
Few people want to do a site wide search and the ones who do will press the input box on the top left. No one expects that ctrl-f will open a site wide search, everyone expects a page search.
If you still want to enable this ctrl-f to enable the site wide search, I suggest making it opt in with the checkbox. It's really obnoxious to have to disable the checkbox.
If regular users find it helpful, maybe advertise this as an opt-in feature?
To be honest, the non-standard behaviour plus strange looking popup confused me. I didn't even notice the tiny checkbox, nor that you could press CTRL+F again to get the standard search behaviour. My mistake, of course, but this speaks of poor UX in my opinion...
Please don't override default keyboard shortcuts. The sitewide search is a nice tool, but if I wanted to do that I would search on your site. Novice and advanced users want CTRL+F to behave as they are expecting, not bring up an unfamiliar (and unrelated) tool. For example Google Sheets also hijacks CTRL+F but at least it replaces it with something that operates extremely similar to the original action.
Why should a browser allow its own shortcuts to be overridden at all? At the very least, some form of warning or permission-granting should be involved.
They're permitted to be overridden so that we can make web applications. It makes sense for sites like Google Docs or Sheets to override many of the defaults as, once loaded, it's replacing a desktop application and the common access patterns of it. It's less applicable (and very annoying) on sites meant for presentation or consumption of information.
That I would agree with 100%. It'd be nice to have a panel of all the shortcuts and their present meaning available, with the option to rebind them or remove site-local bindings.
The user could get the option to prevent (by default) changes to bindings, with the option to permit them on a site-by-site (or even page-by-page) basis; or to allow them by default and then deny them on a site-by-site basis.
Yes. Discourse does this to great effect. It searches the whole “page” by default, when all the content for the “page” isn’t actually loaded in the browser.
The problem is that our fancy new infinite scrolling pages break ctrl-f in browsers, as they cycle content in and out based on the viewport or collapse threads by actually removing the content from the page.
The downside is that the site's built-in search feature is always worse than ctrl-f at finding something on the page. Always. It shouldn't even be hard, but they're always returning garbage like 8 year old posts on completely unrelated articles instead of the stuff on the page you're currently viewing, and advanced mode is usually broken in weird and confusing ways. It seems like web designers are optimizing for the thing you never do.
If you still want to enable this ctrl-f to enable the site wide search, I suggest making it opt in with the checkbox. It's really obnoxious to have to disable the checkbox.