some times letters get deleted while typing in firefox

[Tapas Mishra]

I am having very strange problem.
I am using Ubunu 10.04 64 bit and Firefox 3.6.8
While typing the letters in search box or input box when on a web page
I fill the
required fields while I am typing some thing in the mid of typing
every thing gets deleted
and I have to retype it and same thing in between happens.
Then I again retype it.
Like this the cycle continues.
For example on Top Right hand corner I can see a search box of Google
in my firefox.
Now suppose I want to search "How to write device driver on Linux"
and I start typing
I have typed "How to write device " and suddenly all the text "How to
write device"
gets deleted as if it was selected by pressing Control+A and deleted
(which I had not done)
I again type it and then again same thing happens.
The only work around for this I found is I open gedit and type what
ever I want to type
and Copy Paste that to required search box or input box where ever required.

Some people on this list suggested me to disable Addons. I do not have
any add on installed on my system.
But this problem does persist.I had asked this question earlier and I
am asking again.As this is very annoying experience.

-- 
Tapas