Created attachment 8799264 [details] fb2k.png User Agent: Mozilla/5.0 (Windows NT 5.1; rv:48.0) Gecko/20100101 Firefox/48.0 Build ID: 20160823121617 Steps to reproduce: I clicked on a link that points to a file. FF asked me where I want to save a file to. I selected a folder on a network drive that already contains a file with the same name. FF asked me if I want to overwrite an existing file. I answered Yes. Actual results: The message window appeared (see attach). The existing file (the one that I wanted to overwrite) was deleted. The new file isn't saved. If I try to save it again to the same folder it is being saved successfully. Expected results: The existing file should be overwritten by a new one.
Is it reproducible when saving the file on a local HDD containing the same file?
No. What is more, after successful saving I'm able to overwrite the file as many times as I wish - but only before FF restart. Also, the issue is unstable - sometimes (but rarely) it can't be reproduced. I believe I found the reason - it's Spider Guard, a component of DrWeb anti-virus (drweb.com). If it is disabled the issue isn't reproducible.
Could you report the bug to DrWeb support, please.
I don't think that it's a DrWeb fault. IE could overwrite files under the same conditions just fine.
Did it use to work with previous versions of FF like FF48 or 45? If yes, could you download the tool mozregression to narrow down a regression in FF49(or older). See http://mozilla.github.io/mozregression/ for details to use it. Run the command 'mozregression --good=48 (or any version working)' then copy here the final pushlog.
No, the behaviour of previous versions was the same. I was just too lazy to report this before.
HideTab extension was guilty of the issue. Sorry for bothering guys.
No I was wrong. I have reproduced the bug in 48.0.2 with all add-ons disabled and also in a just created clean profile. Also, I have reproduced it in portable versions 30.0, 40.0 and 49.0.2. The ability to reproduce depends on the size of the file. It is pretty reproducible with 80KB+ file (http://www.nirsoft.net/utils/cports.zip on http://www.nirsoft.net/utils/cports.html#DownloadLinks) - at least 1 time of 3. IE still successfully overwrites the same file 10 times of 10.