Works well so far. I think the number detection could be made better but a good start.
My only real gripe is to do with integration in Google Contacts. When browsing my contacts there Google "helpfully" encloses any phone numbers in a link to Google Hangouts. If I hover over such a number I see a pop up for this plugin but as soon as I move my mouse to try and click the popup, it disappears.
In an ideal world this popup would work and not disappear. In an even more ideal world the Google Hangouts URL would be completely replaced with the relevant URL handler. In a world so ideal it hurts, right clicking on the link would also present the option (as would right clicking on any selected text that vaguely resembles a number, even if it doesn't match the length rules etc).
It works perfectly for me as far as clicking a number and it dialing without any issues. My one problem is it also thinks zip codes, account numbers and misc numbers are phone numbers. It will note a phone listed as (555)555-5555 but won't recognize 555-555-5555. If I increase the "max" number to look for it picks up every account number on the page. So I may end up with 50 clickable "phone" links on a page when there should only be two or three. This has been the best replacement for Telify which is no longer compatible with FF I have been able to find. Just a little more tweaking and it will be perfect.
It doesn't work with my softphone. There are slashes that make it so the number won't dial. The plugin I used to use is no longer working with the new FF but it did not have the slashes. It should be sip:5555555555 but instead is doing sip://5555555555/ If this can be fixed or an option to disable it that would be perfect