"Find" on XML files doesn't always work

Binary package hint: firefox-3.5

When I view an XML file in Firefox, the "Find" feature doesn't always find text.
It seems to have an invisible cursor from which it searches only forwards, so if it correctly finds some text and then I search for a different piece of text that appears earlier, it doesn't find it.

Moving between tabs adds to the problem, for example:
1, open an XML file whose content doesn't contain the string ab.
2. press Ctrl-F and search for ab => not found.
3. open another XML file that contains the string ab.
4. click on Next in the Find toolbar in order to "re-trigger" the search => it does not find!!

Only if I clear the Find textbox and then retype, it will search the from the beginning and find it.
Thank you.

ProblemType: Bug
Architecture: i386
Date: Thu Apr 8 15:11:18 2010
DistroRelease: Ubuntu 9.10
Package: firefox-3.5 3.5.7+nobinonly-0ubuntu0.9.10.1
ProcEnviron:
 LANGUAGE=en_US.UTF-8
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-18.55-generic
SourcePackage: firefox-3.5
Uname: Linux 2.6.31-18-generic i686