Textbox not clickable in Firefox 4?

I'm hitting an interesting problem where two out of three times the search textbox on a datatables table is not clickable (i开发者_高级运维.e. can't focus) using Firefox 4. Note you can tab through to get to the search textbox though. Is this a verified issue with Firefox 4 itself?

Try the searchbox on www.farnell.com

After a fresh Firefox install it works fine the first 3-4 runs, but after that, I cannot focus on the textbox without first going to the search box of Firefox itself. Click that first, and go back to Farnell's search box, everything is okay. Chrome and IE 9 work fine on this.

Sorry, no answer, just a testcase that keeps me from Firefox 4 (which I would prefer if this bug wasn't in it).