Files with the extension of .part is where Firefox saves files it is downloading. After the download is done, the .part is removed. I think the download did not finish, so the file is no good. Download again. Also, open a file browser and look for the downloading file, and check it when the download is done..

Do you otherwise have problems with downloading and saving files?

Note that this can happen if you do not have the required write permissions for the temp folder or for the destination folder. You can try a different (default) download location.

I am encountering the same problem -- though with .qfx files from my bank. This worked fine in Firefox 31 ESR, but since upgrading to Firefox 33.0, I get the "<name>.qfx.part could not be saved, because the source file could not be read" when I attempt to download. (I should add that downloading PDF statements from the same site works fine, and that the qfx downloads work fine in IE and Chrome.)

I tried safe mode, it is still broken. Tried v34 beta, no luck. I reverted to version 31, it works again.

I guess I will stick with the older version until a solution is found...or just use an alternate browser to download my financial data.

http://kb.mozillazine.org/Unable_to_save_or_download_files

Thanks, but I had worked through the suggestions on that page -- without success -- prior to posting here.

https://support.mozilla.org/en-US/kb/cant-download-or-save-files

http://kb.mozillazine.org/Source_file_could_not_be_read

txtechmozilla are you still out there?

To test further, I reinstalled Firefox 33 and did the Reset Firefox procedure. Even after that, I still got the "source file could not be read" error with my bank's QFX download. Next, I completely deleted my profile and started fresh with a new one -- the error still occurred.

I reverted to Firefox 31 (ESR) and it works fine. It also works fine with IE and Chrome. So, if it isn't necessarily a bug, it is the result of something that has changed in the past version or two of Firefox and how this change impacts the browser's interaction with my bank's server.

If you are sure this a bug, this is a link to Bugzilla. Answer the questions as best you can.

http://bugzilla.mozilla.org/

Once you get a report filed, list it's web link here.

I filed a bug report

I saw it. Good luck.