When Firefox restores your session, it tries to use files from its disk cache ("Cached Web Content") and session history file to bring the page back to the way it looked when you left it. Obviously if your goal is to get the latest page at that URL, and not the one you were looking at when your last session ended, this doesn't match your preference.

I don't think this behavior changed recently. Is it possible that you used to block or clear Firefox's disk cache and that's why the pages always had to reload? If you want Firefox to dump its cache at shutdown, you can set that up on the Settings/Preferences page (I'm not sure what it is called in Linux these days). Either:

• "3-bar" menu button > Settings or Preferences
• (menu bar) Tools > Settings or Preferences
• type or paste about:preferences into the address bar and press Enter/Return to load it

In the left column, click over to the Privacy & Security panel, then scroll down to the History section.

Change the selector to "Firefox will: Use custom settings for history"

Tick the last checkbox, labeled "Clear history when Firefox closes" -- Firefox should now enable the Settings button to the right of that line

Click the Settings button and UNCHECK all categories except Cache -- you want to only clear things you are sure you want to dump. Then click OK.

Now when you Quit Firefox, the cache should get cleared. If you let Linux signal Firefox to close itself during a system shutdown, I'm not sure whether cache will get cleared in that case due to limited time.

More info on clearing different aspects of "history": Delete browsing, search and download history on Firefox.

i don't know how i've made this profile to load pinned tabs. its quite an old profile (probably from ff 60 or something). anyway now i have a question:

is it normal to have so many prefs.js in the profile folder. right now i have reach prefs-137.js. don't know why there are so many. use to be just default one.

Firefox creates a prefs-number.js file if the prefs.js file is locked by another program (or perhaps "read only) when Firefox goes to save updates to it. That can happen from time to time for unknown reasons, but shouldn't happen that often.