how to install firefox addon (noscript) on 6.6/amd64?

I'm trying to set up my usual firefox environment on a freshly installed
OpenBSD 6.6 system, and I'm stuck trying to install an addon (noscript).

My starting point was (is) a fresh 6.6/amd64 installation, with the
firefox-69.0.2p0 package installed and firefox otherwise working ok.

My first attempt at installing noscript was to use the builtin firefox
addon search:
click menu icon on top right menubar
--> click Add-ons
--> type 'noscript' in search box, press 'enter'

This failed with the result
> 0 results found for "noscript"
and the red alert box
> ! Invalid "platform" parameter.

Duckduckgo then told me this is a known bug,
https://github.com/mozilla/addons-frontend/issues/4610

My next attempt was to go directly to
https://addons.mozilla.org
and search for noscript there. This found it, and one more click
brought me to
https://addons.mozilla.org/en-US/firefox/addon/noscript/?src=search
I then tried to install ("add") this addon into firefox:
click the blue "+ Add to Firefox" button
--> get permissions-request popup, accept
--> the extension .xpi file is then downloaded to /tmp
(e.g., /tmp/tmp-622.xpi, size 572021 bytes, cksum 3655027406),
but the extension never installs -- firefox just keeps showing the
blue-dot-oscillating-left-and-right spinner forever :(

A bit more web searching led me to
https://support.mozilla.org/en-US/kb/unable-install-add-ons-extensions-or-themes#w_you-are-asked-to-download-the-add-on-rather-than-installing-it
which suggests that I "drag and drop the file into the Add-ons window".
But there's no concept of "drag and drop" in my window manager (twm).

So.... questions:
* How are other people installing firefox addons under OpenBSD 6.6?
* Is there a command-line way to install a firefox add-on if the automagic
install fails?
* If I want to report this bug, should I do so here (ports@) or over
at mozilla gibhub (or somewhere else)?

thanks, ciao,

--
-- "Jonathan Thornburg [remove -color to reply]" <jthorn4242@gmail-pink.com>
"He wakes me up every morning meowing to death because he wants to go out,
and then when I open the door he stays put, undecided, and then glares
at me when I put him out"
-- Nathalie Loiseau (French minister for European Affairs,
explaining why she named her cat "Brexit")