I've been noticing for the last month that after a few hours in a browser window, I'll suddenly have a pinned tab for some random website. Some for promotional things, others in languages I don't understand, etc. At first I downloaded a webpage blocker, blocked the ones that were pinned, and deleted the tabs. However, after a short while (an hour or two) they would appear again in pinned tabs only this time it would say website blocked.

I uninstalled and reinstalled firefox in hopes that would solve the issue, but it is still happening. I unpin the tabs and delete them immediately after I notice them, but they keep appearing. I really like using Firefox and use it often for work, but I'm concerned for my personal and work security. What should I do?