Does that show up on a lot of sites, or just your email page?

If you think it could be injected by an add-on, here's how to investigate. You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. To open that, use either:

• Command+Shift+a (Windows: Ctrl+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. On the right side, find the "Manage Your Extensions" heading.

If there is at least one extension before the next heading -- "Recommended Extensions" -- please continue:

Then cast a critical eye over the list below that heading. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything suspicious or that you just do not remember installing or why? If in doubt, disable (or remove). For your privacy and security, don't let mystery programs linger here.

Any improvement?

It shows up on all my email accounts and also on YouTube as well. I have a MacBook, can't find the "Extensions" or "Manage Your Extensions" any where on Mac.

The Add-ons page is an internal page within Firefox. You should be able to open it by pressing Command+Shift+A. On that page, is there an Extensions category in the left column?

See attachments, don't know what to add or delete?

On the first list, "Manage Your Extensions" - "Enabled", these are all optional things that either you or someone with access to your computer added. None of those come with Firefox. If you are not 100% sure about them, disable them or remove them. I think Grammarly is legit but I would dump the others if I were you.

Thanks, for the advice. I just delete everything but the Gramarly. The icon I want to delete is still there, see attachment.

If you click that button, what happens?

If I click that button, it will show a pop up menu of different icons of social media. But for reason I play around and menage to delete the button. I don' know what I did but it's been deleted.