I use IE7, Firefox and Opera at various times and always found it a nuisance trying to keep them synchronized, even with the various add-ons available.
Thanks to reading help forums like this one I've now bought, and use daily, a great little Bookmark/Favorites manager called LinkStash
It works with Internet Explorer, Netscape, Mozilla (Firefox), NetCaptor and Opera, but it's SEPARATE from them so you don't have to worry about synchronizing all the time. To open a bookmark you can either leave it to open with whatever default browser you had set it to, or right click the bookmark to open it with a browser of your choice.
Its layout is very similar to Windows Explorer with drag 'n drop, copying, sorting, highlighting etc. It's searchable too!
You can download a free 30 day (full version) trial to see if you like it.
Bet you WILL though!
Works in all Windows except '95.
To buy (after the 30 days) it does cost US$19.95 but hey, that's only about 10 quid (UK) at current exchange rates. (About 4 pints of bitter - If you don't live in London!)
One of the best ten quids worths I've ever spent anyway!
I was so SICK of wondering where that half remembered bookmark had gone - maybe I'd saved it in IE7, - or was it Opera? - now where the hell was it! - I DID save it didn't I?
All that's finished now. - I KNOW where it is!
p.s. I honestly have no connection at all to the program makers or vendors. I just love the program and think it should be better known! Please pass it on if you like it.
p.p.s. I prepared this post in a note using my favourite free 'stick-it' note program "stickies"