Could be as I had trouble with this one vendor on-line, just the one, as Amazon and the others seem unaffected. So below is a copy and paste I had with their help desk;
Bruce
Jul 27, 08:20 PDT
Chat started: 2017-07-27 02:50 PM UTC
(02:50:51 PM) *** Help Desk 2 joined the chat ***
(02:51:05 PM) Help Desk 2: Hello Bruce
(02:51:18 PM) Help Desk 2: There appears to be an issue with the browser you are using
(02:51:30 PM) Help Desk 2: Have you tried a different browser?
(02:51:44 PM) Bruce: You have some code in your page with "Proceed to Checkout" that doesn't either want to co-operate with Firefox 54.0.1 or there is a glitch in my copy or maybe I have the security features cranked up too high. Again clicking on that page in FF produced no action. What I had to do was run Google Chrome, which I hate because it is a privacy risk and leak, most people don't know. Copy and paste URLs cross-ways - FF to chrome, which got me to the checkout, then that URL back into FF, after which I could continue, securely, to activate my Paypal account from within Firefox and conclude the transaction. I will report the glitch to John Haller of PortableApps as it is his version of FF I use, not the one directly from Mozilla.
(02:52:39 PM) Help Desk 2: Again, I recommend calling in to place your order over the phone
(02:53:18 PM) Bruce: Well, it is done, can you just confirm, while you are there?
(02:53:53 PM) Help Desk 2: Your order was successful
(02:54:05 PM) Help Desk 2: I see from our records ETA on file for you is between 7 AUG - 14 AUG meaning you could receive your order anytime in between those dates. Once your package ships you should receive an email with your tracking information
(02:55:10 PM) Bruce: Thank You, I will contact the developer of Firefox Portable about the glitch.
(02:55:21 PM) Help Desk 2: No problem
For privacy I will not include the vendor's name here, it is peculiar, but it happened twice, same vendor, for my own records I saved the steps that I went through to complete the transaction.