You're copying a link found in a web page, rather than from Firefox's address bar? Unfortunately, this is a problem between Firefox 45 and Thunderbird 38 and will be fixed in Thunderbird 45 (still in testing now, probably available about a month from now).

For the time being, pasting the HTML into an intermediary application, selecting the HTML there, and copying it again before pasting into Thunderbird appears to be the most commonly employed workaround.

Or if you find it easier to launch the page in IE and copy from there, you can use the Open in IE extension as a way to speed up that process: https://addons.mozilla.org/firefox/addon/open-in-ie/

Thanks for confirming that this is a real problem and not something that I broke. Yes, I am copying a link from a web page, not the address bar. Glad to hear that a fix is under way. And there are work-arounds.

Hi hdtvguy, a user who reported this problem in another thread indicated that Firefox 45.0.2 has resolved the copy/paste issue between Firefox 45.0 - 45.0.1 and Thunderbird. https://www.mozilla.org/firefox/45.0..../releasenotes/

That update should reach most users in the next few days, or you could try to accelerate the process using the "About Firefox" dialog as described in this article: Update Firefox to the latest release.

Please let us know if that resolves the issue for you.

Yes, the issue is resolved. I'm running Firefox 45.0.2 now and the problem is gone. Thank you for your help.