Diễn đàn hỗ trợ Firefox

After a recent update, I noticed that my toolbar changed suddenly. I was able to rebuild it how I like and most of it stays, however, the "Open A New Tab" button refuses to stay where I want it.

Whenever I open a new window of Firefox, the "Open A New Tab" button is found on the leftmost side of my screen beside the new tabs. If I go to the "Customize Toolbar" page, I am able to move it so it stays to the right of the rightmost tab, which is where I want it to be.

Anytime I open a new window, whether it's through dragging a tab onto another monitor, or opening Firefox the first time after turning on my computer, my change gets reversed.

How can I permanently move this button to the desired position?

This did not become an issue until an update about a week or so ago.

It's a bit weird, I got the thing you get when you migrate to a new browser - asking if you'd like to migrate history and bookmarks. I closed it because I've used firefox for years.

When firefox opened proper, I got a tab asking to restore the previous session, along with a "Welcome to firefox" tab. As well I got a few popups for other things, basically just stuff you see when you open firefox for the first time. A couple of extensions opened up a landing page that should only open when you first install them.

All my bookmarks and browser history is there. The settings have all been reset to default. The extensions are there but all of their storage seems to be gone, like my dark reader extension no longer has the exception sites on it. Ublock has the ad count reset and most importantly all my custom rules are gone! I have spent years making hundreds of custom rules, and quite a few took hours to get right. I am sad about losing that.

Does anyone know what might have happened?

When I was looking at my about:config to see I saw these things in the modified settings.

there's quite a few settings here and IDK which are relevant. The ones in the pictures where just the first couple and I show them because they seem to have something to do with this situation "auto migrated" - when it seems like the browser did this because it thinks it migrated, the first screen I got was asking if I'd like to transfer my bookmarks and history (and good thing I closed it,or it might have deleted those too).

In firefox developer edition, when opening a new window of any kind, or when relaunching/opening the app, the new tab button always ends up on the left hand side. Going to the customization menu, I can move the button to the right side (next to the last tab), which is where I prefer it, however when opening any new window the button goes back to the left side

After finding out Firefox was storing over a gigabyte of cookies, I figured it might be wise to set it up to clear them except for sites I used regularly. However, I've recently noticed that Youtube will clear regardless. I've tried entering the domain both as youtube.com as well as www.youtube.com, but my video display preferences aren't retained. This doesn't happen for other sites, like Reddit or Tumblr. What do I need to enter in the exception list to keep my settings?