This bug is not currently tracked.
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:64.0) Gecko/20100101 Firefox/64.0
Steps to reproduce:
I reported over a month ago that the issue described in Bug 1374850 (marked as " RESOLVED INVALID") persists (I'm now using FF 64.0.2 (64-bit) under Windows 10 and its the same). I cannot reopen that, and I don't know that anyone else will see my comment, so reporting here. See also Bug 475896
Example below. If you prefer to avoid PDFs, the problem also occurs with:
1 Visit http://uta-eickworth.de/Wilke%20Tierillustration%20Heft%20Web.pdf
2 copy address from location bar
3 pastes as: http://uta-eickworth.de/Wilke Tierillustration Heft Web.pdf
Should paste as http://uta-eickworth.de/Wilke%20Tierillustration%20Heft%20Web.pdf
That works for me as expected with Firefox64.0.2 on windows10.
I copied both URLs from the URL bar and pasted them in notepad and both URLS had the correctly escaped spaces.
Can you reproduce the problem in the Firefox safemode ?
The problem occurs in exactly the same manner in safe mode.
Please also try a brand new profile. If it works there, one of the browser.urlbar.* about:config preferences might be to blame.
I also cannot reproduce if I copy from the urlbar and paste in another app, like a text editor.
check you didn't set browser.urlbar.decodeURLsOnCopy to true.