Yes, this is normal for how I use Firefox. Or any browser I’m using for ordinary work-day use. I have a couple of tabs open to two different Google email sites (ordinary gmail, and Google Suites, both tabs grouped and minimized), then another group of tabs open simultaneously as I read news, for example. I’ll go to an aggregator, open a tab for every news article I want to read, and when I have a dozen or so open tabs, I’ll pour my coffee and begin to drink it while I read through the tabs.
Somewhere in here - from day to day - I’ll click on a bookmark for Sanityville in my Bookmarks bar.
The deja-vu thang happens (when it happens; it’s not happened in the past 36 hours) I’ve guessed that I’m seeing a page I’ve seen before. In other words, its a page that existed in the past, and is now reappearing.
When I’ve seen it, I click the “Save edit” button, and go on my way - closing the tab in which Sanityville was being viewed. Coming back to Sanityville later the same day - no problem. Until the next day, there it is again!
Except it didn’t happen this morning when I “arrived here.”
It’s not a bother, of course. I have no complaints! I’m reporting this 'cause I do not know how/why/what it might matter to youse guys who tinker on the back end of all this stuff.