You select a page element and generate a link, which you can then share. For someone without the extension, the link will work as normal and just take them to the page, but someone with the extension will have the selected element focused on and highlighted for them.
There's also a repo on GitHub (for now)[1] and I wrote about how I made it[2]. My next priorities are to make it not look like ass and to shorten the links somehow. Let me know what you think.
[1] https://github.com/Rumperuu/Pinpointer
[2] https://bengoldsworthy.net/2018/04/developing-pinpointer/
There's archive sites that do this, without a browser extension, and since it's an archive site instead of a live page, the content won't change underneath the target: http://archive.is/RUyWM#selection-253.74-253.223
(I wasn't kidding about needing to shorten those links.)
I wish Firefox had a permission along the lines of 'Access all data from pages on which I activate the extension', which is presumably all this would need.
[1] https://github.com/Rumperuu/Pinpointer/blob/master/content_s...
EDIT: Or tabs.onUpdated if webNavigation doesn't fire for hash changes[2]
[0] https://developer.mozilla.org/en-US/Add-ons/WebExtensions/AP...
[1] https://developer.mozilla.org/en-US/Add-ons/WebExtensions/AP...
[2] https://developer.mozilla.org/en-US/Add-ons/WebExtensions/AP...
EDIT: I had a look at the manifest.json[1], and it turns out that's the only permission I've requested. Not sure why Firefox says I'm asking for everything and the kitchen sink.
[1] https://github.com/Rumperuu/Pinpointer/blob/master/manifest....
In the Mozilla addons page it just says "Pinpointer error".
In this HN page, it prompts me to select and click a green button, but fails to do anything.
It's an interesting concept, keep going!
edit: Firefox 62.0b9 (32-bit) in up-to-date Ubuntu 16.04, with uMatrix and other extensions running.
extensions.webextensions.restrictedDomains
https://www.metafilter.com/175389/None-Dare-Call-It-Treason#...
