I've met this too yesterday, while running Firefox from the following packages, under KDE 4.8.5 (was latest stable at F16 repo):
- xulrunner-last-21.0-1.fc16.remi.x86_64
- firefox-21.0-1.fc16.remi.x86_64
- firefox-21.0-3.fc16.remi.x86_64

Was not working
- In the search box, pressing [Enter] or using the "Paste and Search" action (no effect).
- Applied to any fresh profile, under normal and safe mode, even tried reboot.

Was still working
- Switching search engines and entering text in the search box
- Using "Search using..." contextual action from selected page content
- Just everything else in my profiles

Self-Fixed™. I had *not* noticed the issue immediately after upgrading to these versions, but several hours later. Hence, I had not suspected the upgrade in the first place and started looking into js prefs and addons, until I realized the issue was also occurring in a newly created profile anyway. Then, several hours later, I noticed the problem was "just gone" without any further action from me in the mean time (?).
- Is there any temp file maybe, which could have tempered with this?
- Does the search box rely on any sort of connection?
  (connectivity has appeared difficult at the same times, but functional overall)

xulrunner-last-21.0-2 and firefox-21.0-4 are available and fix this problem.

Dear Remi,

Could you please tell me what it is you changed to fix this? I am trying to compile my own xulrunner + firefox and I am running into the same problem of the search box not working. I have trouble to understand where the problem comes from.

Thanks

Hi, Remi, sacha

I'm in the same situation as sacha.
I was checked remirepo but Icouldn 't figure out how fix this problem.

Please give me more explain or another hint.