What extensions do you have loaded in your Firefox?

You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+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.

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? Anything you can live without for four hours? If in doubt, disable (or remove). For your privacy and security, don't let mystery programs linger here.

If you want to share a list of your extensions:

You can copy/paste it from the Troubleshooting Information page. Either:

• "3-bar" menu button > "?" Help > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

Scroll down past the first few tables to the "Extensions" heading. Then you can select and copy the table that follows (not the entire page, please, that's too much information) using either Ctrl+c or right-click > Copy and then paste it into a reply. It will be messy, but we're used it.

You can also check out;

You may have ad/mal-ware. Further information can be found in this article;
https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners. Each works differently.
If one program misses something, another may pick it up.