Sometimes just clearing all cookies will not work if one cookie is corrupt or "stuck". Then you need to clear that individual cookie manually. Try using the Manage Cookies and Site Data feature in your Firefox Options, then search for "ebay" and try deleting each of those cookies, then restart your browser.
If that does not help, keep reading:
If things are working in Chrome but not Firefox, you may also have a setting or add-on in Firefox that is interfering somehow.
General suggestions for those encountering problems in one browser:
Disabling ad blockers, pop-up blockers, script blockers or other privacy tools on the error-prone pages can sometimes help; many of those have settings that can cause problems. You may be able to turn them back on once or just selectively disable a critical one on the affected pages.
If you are using Firefox, try disabling Enhanced Tracking Protection on eBay using the shield icon to the left of the page address.
Or try a different browser -- preferably the latest version of a popular browser that you do not normally use and one that has no add-ons or extensions installed. You can try installing an alternative version of Firefox such as Firefox Developer Edition or Firefox Nightly -- either of those will install in parallel with your current browser without affecting it.
