I managed a temporary work-around by re-installing Firefox 4.0 Firefox 4.0.1 was no good because it automatically updated to Firefox 5.0 Fortunately I had saved the installers to disc in April/May 2011, they are not available from Mozilla - and they should be! I had to turn off the automatic update and install feature, this is what caused the problem in the first place. This is a dangerous feature to let loose. All updates should be thoroughly tested that they do not disable important security and other add-on features, or should wait until suitable updated add-ons are available. Kaspersky and RealPlayer are important main-stream add-ons, not trivia. This is a classic violation of software control in design. The latest Firefox 5 "Security Update" urgently needs to be rolled-back across the board and fixed before re-applying.

Ok, now it keeps asking to upgrade to Firefox 5 which I do not want until it is confirmed as fixed (despite turning the update feature off, mutter...) and I notice that Firefox 4.0 is considerably quicker than Firefox 5 was. Go figure. Btw installing FF4 over FF5 keeps bookmarks and links. and I need to work without all these stupid interruptions.