Maybe more details would help,

• presumably you are talking about some sort of customisation you made to firefox ?
• what exactly are "Top Sites"

I must be. I can't recall how I came up with this facility. It's just a page of a selection of frequently accessed sites (like weather) visually represented; all you need do is pick which one to open just by clicking on the image. Much easier than scrolling through a long series of menus to get to the one you want. Sometimes it actually pops up & I haven't a clue how/why, but if I try & get it open, I can't. Pity really, 'cos it's so user-friendly/useful. Phil

You probably had the FoxTab addon. FoxTab hasn't worked for me since Firefox 9?, 10?, 11?... anyway, asof Firefox 13, today, I'm hoping the new built-in Firefox top sites function will replace FoxTab--which I loved!--if only I can figure out how to add sites to the top sites displayed/listed on the new tab.

You can change the order of the boxes on the about:newtab page and drag them to a different position to pin them to that position or you can remove them by clicking the close X of an item to block them.
You can drag a bookmark or history item and drop them in a slot on the about:newtab page to pin them.
Such changes are stored in the chromeappsstore.sqlite file in the Firefox Profile Folder under the pinnedLinks key and blockedLinks key.

@cor-el: Thank You! Your reply, "You can drag a bookmark or history item and drop them in a slot on the about:newtab page to pin them." answered my question & solved my issue!