OK, having installed a previous version of flash, I'm now up to date again. Having looked at the Adobe site, the culprit, at least for me, seems to be the 'RealPlayer Browser Record plug-in'.
Sorry, it's a long time I messed around with HTML:
http://forums.adobe.com/thread/1018071?tstart=0
They advise disabling as follows:
- Launch RealPlayer
- Click the RealPlayer icon in the upper left corner of the window and choose Preferences.
- Choose Download & Recording from the left hand panel
- Uncheck "Enable Web Download & Recording for these installed browsers"
- Click OK and close RealPlayer
- Restart Firefox
Twenty stable minutes and counting...:)
Steve