Do you recall going into about:config and turning on the privacy.resistFingerprinting feature? It blurs images extracted from a canvas, so it can show up in odd places.

If you have enabled that feature and want to keep using it:

While you are on a problem site, is there a canvas permission icon toward the left end of the toolbar? If so, you can use that to give the site permission to extract images from a canvas without blurring.

If there's no icon for it, try the Page Info dialog. While you are on the relevant page, you can call that up using either:

• Ctrl+i (for Mac, Command+i)
• right-click a blank area of the page > View Page Info
• (menu bar) Tools > Page Info

When the dialog comes up, click the Permission icon at the top to show that panel.

Near the top, you'll find "Extract Canvas Data" and you can uncheck the "Use default" box and select the Allow permission. (Note: this permission only appears if privacy.resistFingerprinting has been enabled.)

That change is saved immediately. You can close Page Info and it should be effective on your next upload.

Was that it?

If you would have enabled "Resist Fingerprinting" then your user agent would have changed to Firefox 78 (current ESR), but since this is still 85 (current release) this could indicate something else is going on.

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or userChrome.css is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems