After creating a new profile Firefox will download the GMP and Widevine video plug-ins. Therefore temporary files are getting created: > -rw------- 1 henrik 403751 Jun 6 20:55 tmpaddon > -rw------- 1 henrik 1755276 Jun 6 20:55 tmpaddon-74a9f2 Even after the installation of those plug-ins the temporary files are still present and have not been removed. This is annoying especially for automated tests and those harnesses which have to keep the download of the plug-ins enabled. For example geckodriver via Selenium. Given that for each testrun the harness creates a new profile, the temporary files are getting accumulated until the machine gets restarted. Given that this doesn't happen quite often, a lot of space is taken up by those files. As you can see above for each profile it's 2.2 MB. Is there a reason why we have to keep these files, or was it just an oversight in not deleting them? Chris, as it looks like you have made a lot of changes to the file, including the download via XHR. So maybe you can help?

I'm trying to disentangle myself from media, so I'll pass this ni? onto the media team manager...

Looks to me like the problem is somewhere in here https://searchfox.org/mozilla-central/source/toolkit/mozapps/extensions/internal/XPIInstall.jsm#3614 Henrik is that enough information for you to solve it yourself? If not how urgent is this?

It's not urgent for us. We are going to disable all the plugins anyway via bug 1467700.

Using FF 64.0 (64bit) under Windows 8.1, I just found a 'tmpaddon-nnnnnn' file in Windows' %TEMP% folder. I couldn't delete the file which was apparently in use; the SysInternals' "handle" utility could not show me which aplication/process had it open, but finally I used 'Process Hacker' to show that it was in use by Firefox. I separately copied the fle, peeked at it, saw the "PK" header info and unpacked it using 7-Zip. Three DLLs and a License file gave enough info to google and find out what it probably was. Looking at FF's Tools - Addons, I see that FF has gained an Addon, updated today. Maybe it's the first time my FF has ever had this Addon, I don't know. I have NOT created a new profile in FF though. I'm puzzled why the temporary file is still open. As FF knows the Addon has been installed/updated, that must mean that the contents of the file have been read, unpacked, and something done with them. Why didn't the Addon install/update process close the file after use? Deleting it would have been good too. It would also have been better if the thing had had some sort of obviously Firefox-related name. "Tmpaddon" is not really good enough.