Why did a random web page open when I started Firefox? I never gave it a permission to do so

As it says in the title, when I opened Firefox earlier today, a new tab opened reminding me of a Black November sale for Browsec, a service I’ve never heard of before. Why does this happen? I’m not a control freak, but I also don’t want random pages to pop up when using my browser.

EDIT: Here is a link to the screenshot.

EDIT 2: Quick check at whois.com confirmed that it’s indeed a domain owned by Amazon. I can only guess It’s some promotional deal between Mozilla and Amazon.

I will mark this post as solved since I don’t want to invest more time into this. Thanks for the replies.

I would bet it’s the add-on closest to the hamburger menu in your screenshot. It appears to be the same globe logo.

Extensions can open pages.

I’m on Ubuntu 20.04 and I don’t use any application that would do this.

Here is a screenshot of the page that popped up.

EDIT: Sorry, I don’t have this addon installed.

it wasn’t, I posted link to the screenshot of the page in the comment below.

From your screenshot I see you have an icon in your toolbar (next to the hamburger menu) that looks very much like the Browsec VPN extension icon, and that add-on does currently cause that web page to appear.

You are right and I’m a fool for not seeing that. Thank you.