Comment 8 for bug 428703

I have the same problem as well. I have had it since installing 9.04 32bit. I reformatted and installed 9.10 x64 and the problem is sill present. I opened a bug report with the Firefox folks several months ago but nobody is able to duplicate the problem. The bug can be views here: https://bugzilla.mozilla.org/show_bug.cgi?id=502988. The problem is not present on my wife's laptop with Linux Mint installed. This seems to be a Ubuntu only problem.

I can further say that it has nothing to do with a screen saver or any other plugins. This happens with a fresh install and no screen saver running. To duplicate it simply do the following:

1 Start Firefox
2 Leave machine sit idle for 5-10 minutes.
3 Attempt to type in the URL bar.

At this point the text will auto highlight after about 1/2 second making it impossible to type. Closing Firefox and restarting clears the problem. I have discovered a workaround to be able to type in the address bar without having to restart Firefox.

Quickly type the LAST 2 characters of the address you wish to type. For example if you are attempting to type www.ubuntu.com, type OM. The OM will get highlighted at this point. Press the HOME key then type the rest of the address. This puts the insertion point at the beginning of the line and bypasses the auto highlight. (well, most of the time). This has helped many times when I had tabs opened that I did not want to lose on closing