Welcome to the forums! Can you give an example of what you are bookmarking? Is VOD Video on Demand? and what browser are you using ?
>>After you search for, find, and BookMark a VOD, how can you later go back in and review/select one you have Bookmarked?
Press the Menu button on the remote, then choose Video On Demand (usually the Menu opens with "Video On Demand" selected), then scroll down and choose "My Library". One of the suboptions for "My Library" is "My Bookmarks" and when you choose "My Bookmarks", you will see all the items you've bookmarked.
When you choose a bookmarked item and watch the program, the item will remain in the bookmark list until you choose the "Remove Bookmark" (via the Options button on the remote). When you watch a bookmarked program, it also puts an entry into the "My Rentals" area (another suboption in "My Library")--so the item is "stored" in 2 places "My Bookmarks" and "My Rentals".
When you are finished with the item--don't want to watch it again--from the "My Rentals" list, press OK (remote key), press the "Options" key on the remote and choose "Delete".
I find the FiOS On Demand menu system to be so incredibly convoluted. Comcast's, in comparison, is much more straightforward and much easier to use with significantly fewer remote-key usage required.
Hope that helps...
tlb's answer is very accurate. The only thing I would add is that while STBs share Rental lists, they do not share Bookmarks. I have found that Bookmarks are only stored on the STB that created them. I can't place a Bookmark on the STB in my bedroom and call it up on the DVR in my living room. However I can Rent a program in one room and continue watching it in another.