Q:

Firefox removes href attribute if the link doesn't start with htttp://

If I paste an html link with a href that doesn't start with http:// in an html editor in Chrome or Firefox, then result is not the same. Chrome keep the href attribute but Firefox removes it. 
So if I paste a link (which has this source code <a href="zotero://open-pdf/0_123456" target="_blank">Open PDF</a>) in the HTML mode (not the source code mode) of an HTML editor in Chrome, and then them switch to the source code mode, I see the exact them source code as above. But if I paste the same link in an HTML editor in Firefox, I end up with this source code:
<a target="_blank">Open PDF</a> 

The test can be done with Quackit.com. When I start Firefox in Safe Mode, then the href="zotero://open-pdf/0_123456" isn't removed.
How can I paste a link in an HTML editor in Firefox when its href doesn't contain an http://?

More background: I am creating this link with a python script based on HtmlClipboard

I tried all the solution on that page but without success. My issue doesn't seem to be the same. I don't have any trouble opening a local link with firefox: if I paste zotero://open-pdf/0_123456 in the url bar, firefox open the pdf. I have trouble pasting the html link in an html editor. 

A:

After all, it wasn't caused by Firefox but one of my extension because the problem disappears when Firefox is in safe-mode (on Windows, Windows + R and enter firefox -safe-mode). This doesn't resolve my problem, but at least it answers this question. 
Thanks to jscher2000 for pointing that to me. 

