Our signed xpi extension does not install anymore with Firefox 48

We are distributing with our applications a firefox extension as a xpi file which is install by our installer using the firefox command line.

Our firefox extension is fully reviewed and signed by the AMO site.
Everything was working well until Firefox 47.0.1, but with the new Firefox 48.0.2, we have now instead the error message “Firefox prevented this site from asking you to install software on your computer”.
We are using the command line: firefox.exe -p default extension.xpi (with no firefox process already running)

What is strange is that if we start firefox first and then use the same command line, the extension installation is proceeding normally, installation is not blocked !!!

What has been changed in Firefox 48 in extension management. Is it a bug (as it proceeds normally when firefox is already running) ?

In our case, for several reason due to several firefox profile management, we need to close all firefox process before installing our extension using the xpi file and command line.

Kind regards,

I suggest you look for answers in the Enterprise group. It would also be good to test this in 49 and 50 to see if the problem can also be reproduced. It’s possible that some security change broke this flow.