Every time I click on a fresh page on the forum my Firefox warns me that the site is trying to divert me to another page.Any ideas on this?

When you post (for example) the forum will automatically take you to your posted message. This is a different page than the one you are on so FireFox will not let that happen as you have clicked the "warn me when site tries to load new page" option in FF setup.

Yes Bob. I have got that option set on FF, but in practise, what is happening, when I press mark all topics read(,More than ever these days )Then go back to board index, the warning pops up, if I let it transfer me, it takes me back to the last topic page again.

When you press mark all topics read the site takes you to a page that says all topics have been marked as read. The site then wants to take you back (automatically) to the Index Page. FF will not allow this. You can either click the "allow" on the FF warning or 'return to Index" on the site page - you will end up in the same place which ever you do...