Browser compatibility issues on vendor sites

Had a vendor's order form refuse to submit for 20 minutes before I figured out the issue. Browser compatibility problems on vendor sites are more common than they should be given how simple the forms usually are. Here is what I have run into and how I fixed each one.

Upload failures

Vendor photo upload forms sometimes fail silently on certain browser and extension combinations. My instance was a combination of an aggressive ad blocker and Firefox's strict privacy mode, both of which were blocking the JavaScript that the vendor's upload form relied on. Disabling the ad blocker specifically for the vendor domain fixed the upload immediately. Chrome with no extensions is the most compatible option if you are having upload failures in Firefox.

Form submission blocked

Some vendor checkout forms use a CSRF token or session cookie validation that fails when VPN exit nodes rotate mid-session. If you are using a VPN that rotates your IP automatically, the session token generated when you loaded the form may be validated against a different IP than the one you are submitting from, causing the form to reject the submission. Turning off automatic IP rotation or using a static server during checkout solves this.

Payment page issues

Crypto payment QR codes on vendor sites sometimes load only in specific browsers due to canvas rendering differences. If the QR code is not rendering or is appearing as a blank white box, the issue is usually a browser content security policy blocking an inline script that generates the QR image. Firefox Private Browsing Mode is particularly aggressive about this. Switching to a regular browsing window for just the payment step resolves it.

The general troubleshooting flow: try Chrome with extensions disabled first. If that works, re-enable extensions one at a time to isolate the conflict. If Chrome does not work either, the issue is more likely VPN or network-related than browser-specific.