On Mac, with RTL languages, CMD+Left/Right does the wrong thing

I tried this on google.com (search bar), inbox.google.com (search bar) and facebook.com (write post). Tested only with Firefox 56 and 57. TL;DR: CMD+Right/Left is reversed for text inputs in Firefox in Mac. Steps to reproduce: - Set input language as Hebrew (or any RTL language, I guess) - Go to google.com, write a word in Hebrew (for example: שלום) Caret should now be at the left end of the word, like this: |שלום - Click CMD+Right Expected: Caret goes to the beginning of the word, on it's right, like this: שלום| Actual: Caret doesn't move - Click CMD+Left Expected: Caret doesn't move (it's already at the end of the word) Actual: Caret moves to the beginning of the word, like this: שלום| I've also tried setting bidi.browser.ui to true, but it didn't help.