That is probably an error or change in the message board itself. The preview text is included in the webpage - not generated by the browser.

For example this forum provides such a facility
http://www.prepaidgsm.net/forum/uk-ireland/
Can you see the hover-over text?

Thanks, but it is happening on multiple websites and I can still view the preview on other computers - it's just the one using Firefox where it no longer works. I was hoping there was just a setting that somehow was changed on this one computer.

Can you give an example URL of one that doesn't work in Firefox? (One that doesn't require me to sign in.)

Sure - if you scroll over any of the thread links a preview of the first post should appear without the need to clink on the link.

http://www.disboards.com/forumdisplay.php?s=&daysprune=30&f=119

Issues with tooltips not working properly have been reported to be caused by the Google Toolbar (Tools > Add-ons > Extensions)

You can check if there is an update available that fixes that issue.

You can try to uninstall and reinstall the latest GT, that has been reported to work.

• http://www.google.com/tools/firefox/toolbar/FT5/intl/en/
• http://tools.google.com/tools/firefox/toolbar/FT5/intl/en/install.html

Works for me in Firefox 4b7 on Linux. If I hover over 'Post your DVD pictures' I can see "I saw the cruise..." Presumably it doesn't work for you on Firefox 3.6.7 on XP

So I tried Fx 3.6.12 on XP (why are you using 3.6.7 - it's out of date?) and it still works.

First of all, I should update to 3.6.12 (Help > Check for updates) If it still doesn't work there's something wrong with your configuration. Maybe an addon?

See here
http://support.mozilla.com/en-US/kb/basic+troubleshooting

Thanks. I'll try the upgrade. It did work until last week and then suddenly stopped working. That's why I was looking for a setting to change. I have not installed any recent add-ons.

Thanks for taking a look.

I'm now on 3.6.12 and have reinstalled Google Toolbar, but no luck with the rollover view.

Does it work if you disable/uninstall Google Toolbar - to see if that's the problem?

No, it still does not work even when Google toolbar is disabled. It does work with Safari, Google Chrome, Explorer and Opera but I'd rather use Firefox.

Just to recap:

I see tooltips in the disboards link you gave with Fx 3.6.12 on XP.
You don't see them with the same versions.
A lot of people report that this problem can be caused by Google Toolbar.
I don't have Google Toolbar.
You do.
But if you disable Google Toolbar you still see the problem.

I've googled a bit and can't find any other causes of this. My suggestion now is to uninstall Google Toolbar and see if the problem disappears. If that doesn't work then try safe mode as described here:
http://support.mozilla.com/en-us/kb/basic+troubleshooting#Troubleshoot_extensions_and_themes

Thank you. That solved the problem. Thanks so much for all of your help and suggestions!