OK, I suspect this might be a Firefox question/issue as much as a Straight Dope issue, but it seems to happen here more than other sites I visit.
If I click on a topic and go forward to the thread page, and then read the posts, I often have to hit the back arrow two, three or more times to go back to the page that shows the various threads. If I right click the back arrow, it shows the same visited page two or three times as past web pages.
I am running Firefox version 66.0.4, and have very few extensions, add-ons or plug-ins. I used to use an adblocker, and think I probably should be using one, and also think one might fix this problem, but I don’t know which one to use.
I’m not going to argue with your statement that the board has been plagued with this sort of thing over the years (because it has), but in more recent times we have switched so that we aren’t using the bottom-dwelling ad providers that we used to use. Even with the best of ad providers something malevolent can sometimes sneak in, but incidences here of that sort of thing have dropped off dramatically now that we use better ad providers.
I know it’s still a knee-jerk reaction by many here to assume malware, but I wouldn’t immediately jump to that sort of conclusion these days. In the past? Sure. Today, no.
A lot of times this sort of thing is ad related, but it’s usually not malicious. What an ad provider may do is provide a URL for an ad, but then they have that URL redirect to whatever ad they actually want to serve up (there are different ways of doing this so this isn’t universal). Your browser redirects to the second page where the actual ad is, so when you hit the back button you end up going to the redirect page which then bumps you forward to the ad, so you hit the back button again which again forwards you to the ad, and so forth. If you hit the back button quickly enough you can usually get past the redirects and get back to where you started. I personally find it quicker to right click on the back button and select the page before all of the redirect nonsense to get back to where I want to be.
This happens all over the web, and definitely isn’t unique to us. It is very common on news sites, since news articles will often redirect to a later article with updated info whenever you have a breaking news situation.
It’s common enough all over the internet that I know at one point the Chrome folks were debating implementing a change to their back button so that it would automatically skip over redirects so that sites couldn’t effectively hijack your back button. I don’t use Chrome so I don’t know off the top of my head if they ever implemented that or not. These days, if Chrome does something, Firefox typically follows suit.