I assume you have already done a proper Forum Search for your model number in case other people have already answered your question ?
If so and that didn't help then check out this thread: https://community.sling.com/thread/3300?tstart=0
Come back if it that doesn't help either.
(BTW, I have no problem controlling my Verizon FIOS by selecting Verizon as the manufacturer. What are you selecting ?)
I understand that you are unable to control your Verizon FiOS box via the Slingbox/ SlingPlayer. Have you tried selecting Motorola QIP 6416 (DVR)? This is a common FiOS remote that works upwards of 95% of the time. It is important to select the one with "DVR" in parenthesis as there are a few QIP 6416 options.
If the issue persists beyond that, you can also submit a request in our Enhancement Requests and Product Feedback section right here in the forum. You can also always check in on the most recent updates (to remotes and more!) in our What's New section. We do have a team which is adding remote controls to our database from the feedback in this community.
Hope this helps!
The Sling Moderation Team