The risk with paid Forefox will be privacy loss, because the app will need to verify somehow the paid status. So there will be some unique, personal licence on the device and Mozilla can identify users using payment info.
The licence will be likely checked via remote API on app start.
Not trying to single you out here, I want to argue against how standard it has become to require a license server. A license server puts an expiry date on the software at an unknown point in the future. At some point the binary you downloaded after you paid for the software will stop working because the server got turned off, changed API, your internet connection is down, your local CA store got corrupted or any other kind of problem in the huge list of dependencies that goes into making a secure API call over the internet. Sure, you can put in safeguards against all kinds of issues, but that also comes at a development cost and you can never reach a point where the software will just continue to work, no matter what.
Even if you, as the company selling the software, can accept all of the above, a license server still is a liability. You sold someone a product and now you need to keep a public API running "forever" (as defined in your legalese). If something goes wrong on your end you are now denying the product you already sold to your customers who already paid for it. I know this is in the end all mitigated by some legalese, which is a whole different can of worms. You also need to make sure your license API is secure and can not leak user data or be twisted into exploiting your software during license checking. There is an ongoing cost to keep the infrastructure running.
As a sibling comment pointed out you can use local only license management like license keys or just nothing like WinRAR or FUTO Keyboard[1]. Yes, you will get users not paying for your software, there will be keygens out there. But even if you use a remote license check, there will be cracks on day 1, if your software is popular enough. I know this is an old and flawed argument, but if someone is willing to navigate a website full of malware infested, blinking ads to avoid paying for your software, they probably would not pay for it anyway.
As an example of what the end stage of hooking up every software to a remote API looks like, Stop Killing Games [2] has done a great job of highlighting just how bad it has gotten in the gaming market. I know there have been some heated discussions around the movement, but the core idea of being able to keep using the software you paid for, is something I absolutely support.
[1] https://keyboard.futo.org/
[2] https://www.stopkillinggames.com/ https://hn.algolia.com/?dateRange=pastYear&query=stop%20kill...
Sell license keys... no need to check online.
Anyway the boat has sailed here as every browser connects to dozens of places automatically and if you go to any bigger site you are basically cyber attacked so advertising companies can fingerprint and track you.