temporary fix for disabled Firefox extensions

[mirimir at riseup.net (Mirimir)]

| All extensions disabled due to expiration of intermediate signing cert

https://bugzilla.mozilla.org/show_bug.cgi?id=1548973

See https://news.ycombinator.com/item?id=19823928 for workarounds in
MacOS and Linux.

I posted to tor-talk, but my account may be blocked. So maybe someone
could post if it doesn't show up soon.