Sorry, it's my extensive schooling in the Slip Mahoney School of Shotgun Linguistics.

It's related partly to theGoogle site verification where something is blocked and may even be something the 'zine does in the manner of temp tracking blocked by either the new setting under /Privacy & Security/Block cookies and some website data.
There is a warning May cause websites to break

Hello Grumpus,

You have the following in your last post (line 4):

Grumpus wrote:Not to cast dispersions but...

I think what you really mean is 'aspersions'!

Regards,

Dave.

Problems are definitely linked to some additional crap loaded with the Google advertising which when blocked allows the free navigation.
This also occurs with some image site links and also some links where some content may have been blocked (trackers, etc.).
I do not think the posting of a link only without some load feature should be causing this but found out through blocking.
Not to cast dispersions but it may be related to the changing of acceptance by Google of http sites.

Method to repeat result:
Load a page where the problem occurs.
Change your filter or settings regarding Google in uBlock, NoScript or whatever you use to block ad content.
You should be able to navigate when the page reloads.
As fas as I remember there's always been issues with some of the Google ads with advertisers taking advantage of slight weaknesses but this seems to be a bit more.
I used a basic Google.com but there are a dozen or more Googles which do not cause the affect.

This is not affected by the removal or disabling of NoScript, again only certain threads. Makes no sense as some threads have no additional links.

Update on the how and why:
It looks like this is due to something which was placed in the Profile's /Storage/Default folder and is related to about-newtab and some form of other extension which appears to be invisible. (doesn't show in about:support
It's beyond me why or what. It also appears google-analytics is somehow involved and the permission level of access to the SiteSecurityServiceState file in the Profile.
I tested this several times on threads where entry locked up the forward and backwards buttons and only allowed the link in the drop down or horizontal link list near the top of the page.

This has been going on for a while now.
Mostly with the SeaMonkey General, Firefox General and Tech forum threads.
Opening an individual thread requires using the navigation list in the bottom right as the back button will not function.
This seems to be more site specific but it's seems to be more frequent lately.
This happened before the update to 60 and is separate from the double and triple click issue in the Firefox Support forum.

Appears to only be certain threads, re-checked and it is still occurring. It may have something to do with links in posts.
Best Guess????