After updating two distinct Macs (a MacBook Air and a Mac Mini, both using the same iCloud account) from Mavericks to Yosemite, I noticed the following weird bug: All keyboard shortcuts in Safari and Firefox (not in Chrome, nor in any other app I've tried) have stopped working. When using a shortcut in Firefox, the corresponding spot on the menu bar is briefly highlighted (for instance, ⌘T flashes File), but nothing else happens; in Safari, not even this menubar flashing occurs.
Weirdest of all: on both browsers, if I first open a menu by clicking on the menubar, then any shortcut works (while the menu is open).
Question: Has anyone else encountered this bug? What would you recommend? Should I notify Apple somehow?