Having been told where Twitter should be it was easy to switch on Inspector and open up the innards:
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At the bottom of the upper window I can see the forum page asking my Browser to open a frame containing data populated by querying platform.twitter.com.
Then the error messages blocked in yellow below include 'Loading failed for … platform.twitter.com …'
Load requests for connect.facebook, googlesyndication, ads.mytimemedia and crazyegg.com also failed; they are all trackers. These naughty load requests were tolchocked in the yarbles by my privacy protections. This is good – I do my level best to prevent websites tracking me lest the information they collect be misused. Neil's link to twitter isn't a tracker but it looks enough like one to get the chop.
I could open the door to twitter by changing my privacy settings. No need, I can go direct to Model Engineering tweets on twitter at any time if I choose to. The difference is between me explicitly deciding to use twitter (for example by clicking V8Eng's link), rather than twitter silently becoming part of a forum page, which might be a privacy intrusion.
Panic over.
Thanks,
Dave
PS I'm having minor bother with Firefox too. I guess it's bugs in the latest version which included major changes.