The only issue is that in Firefox, it is only equivalent for the first search; once you close the bottom bar, subsequent F3/CTRL-G just do "find next occurrence" and do not display the bar anymore. Chrome always displays the search input on the other hand.
Edit: since talking shortcuts, in Firefox ' (apostrophe) is like CTRL-F but searches only hyperlinks (and you can cycle through in case of multiple matches with F3/CTRL-G) which is extremely useful for quickly navigating pages via keyboard only.
0: In Google Sheets, for example, Ctrl-g opens the JS-driven find bar, or, if it's already open, advances the match.
Unfortunately, Alt+F is trivially overridable by web pages (Twitch.tv in this case -- to move to the search bar), so that doesn't really work.
Chromium devs have no idea what the impact of their decisions are... and judging by the issue trackers they don't care.