I had been facing this trouble since yesterday night when suddenly after restart the mostly used firefox keyboard shortcut Ctrl+K started behaving in a different way, instead it should place the cursor in the firefox search box it started opening firefox search page at google. I also noticed that this things specially happened after a small update to firefox.
After a long time googling I was not able to find the solution to this problem, so I decided to reset the search box on the firefox and it worked.
Let me tell you the step by step procedure to fix this if your are facing the same issue in any version of firefox.
In order to fix the problem of malfunction of firefox keyboard shortcut Ctrl+K, follow the procedure given below
1. Right click on the File Menu toolbar in firefox and select customize
2. Drag the search Bar off the toolbar on firefox ( remove it entirely )
3. Now, drag it back from the customize toolbar windows to the firefox frame where it was before
4. That’s it done, its fixed now