rss – Unwanted tabs when opening a Firefox window

Since Firefox 89 (maybe 89.0.2), whenever I start Firefox, or even a new window (Ctrl+N), it starts with a few annoying tabs open, always the same. They are not my previous session.

Most of them are the search shortcuts I set up with wordreference (so you can type in Firefox search enes dog (english-espaƱol) and it will give you the translation perro).

One of the tabs is a website with a RSS feed I fiddled with long ago but never used (Could be here for another reason but I suspect strongly the RSS is why it shows up).

And a few others are websites I know, but have no idea why they show up at start.

When booting Firefox, my pinned websites are still here as they should, along with those unwanted tabs. My browser never did this before.

How can I stop those tabs from appearing when I start Firefox ?