In the picture, if you click on the green writing, you should see some permissions for the website. It should have notifications or something similar, which you can grant the website to pop-up.

actually it has permissions to send me notifications from the twitter page

Before resetting anything, try using CCleaner to clean up cookies, and cached files might help you. Otherwise, the only other solution is reset/reinstall.

Maybe do a complete reinstall?

sorry but I don't think you understand we're talking about "Firefox for Android" in this section

I am more than aware of that. CCleaner has a version for android, and complete browser reinstall won't hurt :)

ahh, ok

I'm using ccleaner already to clean up cache, I didn't know it can clean cookies, I'll try it and then I'll check the browser and I'll let you know, thanks