PMJBG said

I'm pretty sure that Mozilla has stored the address somewhere but I have no idea how to get rid of it.

Hello PMJBG,

Would you check this please :

3-bar menu (or Tools) => Options => Privacy & Security

Under "Forms and Autofill" click on "Saved Adresses ... "

When you highlight an address, you can click on the "Edit" button at the bottom.

Does that work ?

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

Thanks for the advice.

I can't find "Forms and Autofill". It doesn't seem to be in "Privacy..etc", at least nowehere I can find it, so I've deleetd all cookies for anything to do with eBay...again. I don't hold out much hope. I'm also removed my saved eBay lagin details.

As far as I'm aware I haven't got anything unusual installed like Advanced SystemCare.

I'll have to wait a day or two to see if it works. I'll see what happens when I restart the machine.

PMJBG said

I can't find "Forms and Autofill". It doesn't seem to be in "Privacy..etc", at least nowehere I can find it,

Would you try this please :

Type in the address bar about:config and press Enter (ignore the warning)

Type in the address bar and look for the preference :

extensions.formautofill.available

Make sure its value is set to on.

If you had to change the value, then close and restart Firefox.

Any difference ?

I forgot to ask :

Are you using the en-US Firefox version ?

See : https://support.mozilla.org/en-US/kb/automatically-fill-your-address-web-forms

As far as I'm aware I'm using the UK/GB version. I've tried the above and changed it to a tick. Let's see what happens.

For the record, it's not an autofill address as such. eBay just seems to remember the previous address whenever you search for something.

Correction. I'll try again tomorrrow. It might have worked.

Bummer  !

It was a bit premature to mark my post as Chosen Solution .....  :(

You can remove that mark by clicking on the "Undo" button to gthe right of that post.

Probably a redundant question : did you try to toggle the value of the preference on the "about:config" page  ?

I just did some more searching and I found this :

https://www.ebay.com/help/account/changing-account-settings/changing-account-settings?id=4193

Also :

https://community.ebay.com/t5/Selling/Change-item-location/qaq-p/22193814

And :

https://itstillworks.com/change-item-location-ebay-20766.html

Any good ?

I clicked on the wrong button.

All the addresses in my eBay account are correct, or more to the point the address it keeps changing too is not on my account anywhere and hasn't been for years. I even phoned up eBay customer services to check so I'm pretty sure there's something in the back of Firefox doing it.

PMJBG said

Correction. I'll try again tomorrrow. It might have worked.

    Well, let's wait and see - please keep us posted, will you ?

I think I've worked out what it was. I have a bookmark to an eBay search I make relatively regularly. As long as I didn't use that bookmark it stayed as it should be, but if I went to it would change the address for that and every other page. This explains why it seemed to reset so randomly. Sometimes a week or more might go past without me looking at it. I'll stop using that bookmark and see what happens.

That just might be it - good for you to have figured it out !

Once you know for sure that this solved your problem : please mark
your own (last) post as Chosen Solution, will you ?

(it's the "Solved the problem" button to the right of your post)

Note that is is possible that the bookmark includes GET data as part of the URL or hidden POST data in case you bookmarked a link that was generated after clicking a form on a web page. You can check the location field of the bookmark to see if anything is appended (?xxx=xxx) to the link that looks like an ID or location. You can consider to remove the old bookmark and create a new bookmark (check the URL in the location bar for possible parameters appended via ?xxx=xxx).

Ok. I reckon that s it. The bookmark kept resetting the address without me realising it.