Keyboard shortcuts not working in Safari and Firefox after update to Yosemite 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?
I have had this exact problem for weeks, and it's been driving me crazy, but I've finally found a solution. I found this thread on the Apple Support Communities, where “stevendeluxe” says the following:


  Problem fixed!
  I compared the system preferences for each user and found out that I had several languages activated in the language/region settings. So I deleted the language adding the option "list sort order". This option wasn't activated in my test account.
  
  You have to try which language is the "bad one" on your system (In my case it was "german"...haha) and delete it. UPDATE: I've tried to re-add the deleted language and still safari works fine.


I did the same, went to “Language &amp; Region” in OS X System Preferences (found in the Apple menu at the top left of the screen), and removed two languages I'd added as a lark (Swiss German and Klingon, to be precise), and after restarting the computer (which OS X requires if you remove the primary language), all my keyboard shortcuts work again. Joy and jubilation. 

I hope this works for you, too.