[CentOS] Firefox plugins gone (but only for one user)

Hi gurus
I have a CentOS 5.2 current x86_64 that has Thunderbird and Firefox 
working well for one user account (my wife) but will not play nice for 
my account.
I have uninstalled thunderbird and firefox (via yum) and re-installed - 
no change.
I have just wiped the .mozilla folder and started afresh, but it still 
shows no plugins, yet the /usr/lib/mozilla/plugins/ has the 
libflashplayer.so link etc.

How does all this stuff get hooked up.

I have previously installed firefox direct from their site and not used 
the CentOS supplied rpm, but now that RH say the light and provides a 
current version, I use the yum process to get my firefox installed.
Everything was working a week or so ago, but when I tried fixing things 
yesterday, all went rapidly pear shaped.
In firefox I pressed the Check Now button under Firefox > Preferences > 
Advanced > System Defaults and now its gone and lost all my plugins
Any idea how to get them back?

Looking on the support.mozilla.com/firefox site provides little linux 
help and seems oriented to windoze users.
Appreciate some insight from those who know how this distro hangs it all 
together.
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