This is a classic dilemma for those who suddenly have cash to work with, and a good problem to have. Both strategies will increase your 'stache and get you closer to FIRE, and neither is wrong. You should choose what feels right to you.
If you pay off the mortgage, you will have less cash flow in the short term until you pay it off, when you will suddenly have a metric buttload of cash flow. You'd need enough cash reserves to get you through emergencies, and in a real pinch you'd probably be looking at a HELOC or similar borrowing. If it's a big goal of yours to be debt-free, paying down your debt is a huge deal. If you have less than 20% equity right now, paying down the mortgage until you have 20% equity gives you the added benefits of eliminating PMI and giving you protection against becoming underwater if housing prices sink, letting you sell without having to pay the difference if you wanted. There's a good chance that the mortgage interest deduction won't be a factor for you, since an 83k mortgage is small, and you will probably still be using the standard deduction, or very close to it.
If you increase investments to retirement, you will likely build your 'stache a little faster on average, as you can expect to grow the money you put towards this at an average-over-time but volatile-in-the-near-term 7-8%, rather than the guaranteed effective 4.75% stache growth from paying the mortgage. If you have a high risk tolerance, this is mathematically smarter. If the idea of seeing your retirement accounts drop 40% in a year makes you want to sell sell sell, you may want to stick with the mortgage. If you need to access this cash, a Roth IRA is good (without taking the tax considerations into play), as you can access the contributions tax-free.
If it was me, I would see how much extra I could put towards the mortgage, plug it into a mortgage calculator, and see how long it would take to pay off. If I could get there quickly, I'd probably do that. So let's say you can put an extra $1,200 towards your mortgage. You could pay off your 30 year, $83,350 in less than 4 years. I'm pretty risk tolerant, but the idea of being free and clear on a house in 4 years sounds pretty amazing. If all I could spare was an extra $200/mo, it would be a 15 year payback period. Still nice, but that carrot is far away -- I'd probably invest then.