sometimes it is impossible to select from right-button or popup menu by mouse, but still possible by arrows

[jevgtv]

sometimes it is impossible to select from right-button or pop-up menu by mouse in firefox 4.0, but still possible by arrows.
Sometimes switching between open windows and returning to firefox helpes.
The problem exists on one machine more with the same software.

ubuntu 10.04
4.0+nobinonly-0ubuntu1~mfs~lucid1

/.
/etc
/etc/apparmor.d
/etc/apparmor.d/disable
/etc/apparmor.d/usr.bin.firefox
/etc/apport
/etc/apport/blacklist.d
/etc/apport/blacklist.d/firefox
/usr
/usr/bin
/usr/bin/firefox
/usr/lib
/usr/lib/firefox-4.0
/usr/lib/firefox-4.0/application.ini
/usr/lib/firefox-4.0/blocklist.xml
/usr/lib/firefox-4.0/chrome
/usr/lib/firefox-4.0/chrome.manifest
/usr/lib/firefox-4.0/chrome/icons
/usr/lib/firefox-4.0/chrome/icons/default
/usr/lib/firefox-4.0/chrome/icons/default/default16.png
/usr/lib/firefox-4.0/chrome/icons/default/default32.png
/usr/lib/firefox-4.0/chrome/icons/default/default48.png
/usr/lib/firefox-4.0/components
/usr/lib/firefox-4.0/components/binary.manifest
/usr/lib/firefox-4.0/components/libbrowsercomps.so
/usr/lib/firefox-4.0/components/libdbusservice.so
/usr/lib/firefox-4.0/components/libmozgnome.so
/usr/lib/firefox-4.0/components/libnkgnomevfs.so
/usr/lib/firefox-4.0/crashreporter
/usr/lib/firefox-4.0/crashreporter-override.ini
/usr/lib/firefox-4.0/crashreporter.ini
/usr/lib/firefox-4.0/dictionaries
/usr/lib/firefox-4.0/distribution
/usr/lib/firefox-4.0/distribution/distribution.ini
/usr/lib/firefox-4.0/distribution/searchplugins
/usr/lib/firefox-4.0/extensions
/usr/lib/firefox-4.0/firefox-bin
/usr/lib/firefox-4.0/firefox.sh
/usr/lib/firefox-4.0/icons
/usr/lib/firefox-4.0/icons/document.png
/usr/lib/firefox-4.0/icons/mozicon128.png
/usr/lib/firefox-4.0/libfreebl3.chk
/usr/lib/firefox-4.0/libfreebl3.so
/usr/lib/firefox-4.0/libmozalloc.so
/usr/lib/firefox-4.0/libmozsqlite3.so
/usr/lib/firefox-4.0/libnspr4.so
/usr/lib/firefox-4.0/libnss3.so
/usr/lib/firefox-4.0/libnssckbi.so
/usr/lib/firefox-4.0/libnssdbm3.chk
/usr/lib/firefox-4.0/libnssdbm3.so
/usr/lib/firefox-4.0/libnssutil3.so
/usr/lib/firefox-4.0/libplc4.so
/usr/lib/firefox-4.0/libplds4.so
/usr/lib/firefox-4.0/libsmime3.so
/usr/lib/firefox-4.0/libsoftokn3.chk
/usr/lib/firefox-4.0/libsoftokn3.so
/usr/lib/firefox-4.0/libssl3.so
/usr/lib/firefox-4.0/libxpcom.so
/usr/lib/firefox-4.0/libxul.so
/usr/lib/firefox-4.0/omni.jar
/usr/lib/firefox-4.0/platform.ini
/usr/lib/firefox-4.0/plugin-container
/usr/lib/firefox-4.0/plugins
/usr/lib/firefox-4.0/searchplugins
/usr/lib/firefox-4.0/xulapp-profilemigrator
/usr/lib/firefox-addons
/usr/lib/firefox-addons/extensions
/usr/lib/firefox-addons/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}
/usr/lib/firefox-addons/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}/icon.png
/usr/lib/firefox-addons/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}/install.rdf
/usr/lib/firefox-addons/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}/preview.png
/usr/lib/firefox-addons/plugins
/usr/lib/firefox-addons/searchplugins
/usr/lib/firefox-addons/searchplugins/common
/usr/lib/firefox-addons/searchplugins/en-US
/usr/lib/firefox-addons/searchplugins/en-US/amazondotcom.xml
/usr/lib/firefox-addons/searchplugins/en-US/bing.xml
/usr/lib/firefox-addons/searchplugins/en-US/eBay.xml
/usr/lib/firefox-addons/searchplugins/en-US/google.xml
/usr/lib/firefox-addons/searchplugins/en-US/wikipedia.xml
/usr/lib/firefox-addons/searchplugins/en-US/yahoo.xml
/usr/share
/usr/share/applications
/usr/share/applications/firefox.desktop
/usr/share/apport
/usr/share/apport/package-hooks
/usr/share/apport/package-hooks/firefox.py
/usr/share/doc
/usr/share/doc/firefox
/usr/share/doc/firefox/MPL.gz
/usr/share/doc/firefox/README.Debian
/usr/share/doc/firefox/changelog.Debian.gz
/usr/share/doc/firefox/copyright
/usr/share/lintian
/usr/share/lintian/overrides
/usr/share/lintian/overrides/firefox
/usr/share/man
/usr/share/man/man1
/usr/share/man/man1/firefox.1.gz
/usr/share/menu
/usr/share/menu/firefox
/usr/share/pixmaps
/usr/share/pixmaps/firefox.png
/usr/share/pixmaps/firefox.xpm