"Secret-Squirrel - I gave tried Crucial System Scanner Tool but by computer is too old (Windows 2000). I don't feel happy opening machine. Any more thoughts?"

OK then, let's make a start with my second idea:

1) Close all visible program windows so that you only have Windows and Firefox running.

2) Go back to Task Manager's "Performance" tab and note the Commit Charge (K) Total value - make sure you include it in your reply.

3) Click the "Processes" tab then click the "Mem Usage" column heading button so that the processes using the most memory are at the top.

4) Reply and tell us the most memory-hungry processes - you'll need to include the process name and the amount of memory it's consuming.

"Results on task manager are: Firefox 111670"

That one bit of information is actually enough. It shows that Firefox is using 111MB out of a total of just 196MB.

Now, I don't whether that's to be expected for Firefox 3.0 on a modestly-specified Windows 2000 PC. It does however sound like it's using way too much available RAM. Here are a few suggestions for you:

1) Are you running any Firefox add-ons that you think could be causing these memory problems? If you find something suspicious then disable it or remove it.

2) Instead of Firefox, see if you get on better with Internet Explorer. which you'll find is already installed.

3) Try a different browser such as Opera - it's about the only new one that supports Win 2000. It gets good reviews too.

4) If you've still got the setup file for your Firefox 3 then backup your bookmarks and uninstall Firefox then re-install it - perhaps that'll help.