Have you installed any freeware lately? You Firefox is infected with several Spigot extensions that often arrive as part of a bundle, including Searchme. Time for a major cleanup!

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

In the left column, click Extensions. Then cast a critical eye over the list on the right side. All extensions are optional. If in doubt, disable or if possible, remove.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Any improvement?

By the way, your Question Details > More System Details also shows an optional settings file named user.js file in your profile folder (personal settings folder). Firefox uses the settings in that file at startup to override your saved preferences from the previous session. Unless you created that file yourself, it may contain unwanted settings from an add-on or external software.

You can check for and remove the file using the steps in this article: How to fix preferences that won't save (there's a specific section on user.js files).

While you're at it, maybe supplement your regular security software with this on-demand scanner: https://www.malwarebytes.org/antimalware/mac/