Re: Retrieving a webpages shows a blank screen when a 4xx HTTP status is returned. Not helpfull.

On 20 Jan 2021 22:09:14 +0100 R.Wieser wrote:
>Dave,
>
>> <https://addons.mozilla.org/en-GB/firefox/addon/http-status-code/>
>
>Thanks. Alas, FF 52 thinks its corrupted somehow - probably too new (I saw 
>some file extensions in that XPI that I do not recognise).
>
>I will see if I can make sense of it, and if I can back-port it to a XUL 
>style addon.

'Corrupted' often means it doesn't like manifest.json. I think Fx52 
supported WX but may not support all the manifest keys or APIs though the 
latter woukd give a js error I think.

Try an earlier version.

Try removing the signing stuff. You may have to change a pref to allow an 
unsigned addons.

You can't convert it to a xul addon.
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