User Agent: Mozilla/5.0 (Windows NT 6.1; rv:18.0) Gecko/20100101 Firefox/18.0 Build ID: 20130208042018 Steps to reproduce: visited an http web page (not https) clicked on URL bar pressed Shift+Del opened Notepad pressed Shift+Ins Actual results: The contents of the URL bar (which did not include “http”) was pasted into Notepad /verbatim/. Expected results: “http” should have been added somehow, or shown in the URL bar to begin with.
My user agent is different because of the Blender add-on. I am running 20.0a2.
This apparently has to do with the way you're copying. When using right click > copy or ctrl-c, the http:// is added. You can also disable the feature of hiding http:// by going to about:config and setting browser.urlbar.trimURLs to false. Apart from those workarounds, this of course looks like a valid bug (I can reproduce). If you set the component to "Location bar" in the bug details, a developer will probably notice it easier :)
bug 666964 fixed this for Ctrl C copying, changing the summary to reflect the key combo mentioned in comment 0. The current workaround is to go to about:config and change the value of browser.urlbar.trimURLs to false