Usually, all installed extensions will be displayed on the Troubleshooting Information page. Either:

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

Scroll down and below the Extensions heading, they should all be listed there. Can you find it?

(The difference is that extensions can hide themselves from the Add-ons page, but they shouldn't be able to hide themselves from that page.)

If still no luck, we can look for Firefox's extensions database file and see whether it's listed there.

Back toward the top of the Troubleshooting Information page, in the first table, click the "Show Folder" button. This should launch a new window listing your settings files.

Scroll down and find extensions.json and make a copy somewhere convenient, such as your Documents folder. You can close out of the Windows Explorer window after that.

Back in Firefox, open that copy of extensions.json in Firefox's "Scratchpad" tool as follows. Launch the Scratchpad from the Developer menu, either:

• "3-bar" menu button > Developer > Scratchpad
• (menu bar) Tools > Web Developer > Scratchpad

Use the Open button on the Scratchpad's toolbar to open the backup copy of extensions.json and then click the Pretty Print button on the toolbar to re-layout the data in a more readable format.

Then use Find (Ctrl+f) to search for some part of the name of the unwanted extension, and you should see various information about it. The descriptor gives its location on disk. (The \ in Windows folder paths is doubled in this file due to the way it is processed. When exploring your disk, read \\ as \.)

Can you track it down? Please post the path for future reference if you find it.

Note: you don't need to save the changes to the file when you exit unless you want to keep the "pretty" version for future reference.

By the way, many malware cleaning programs can remove bad extensions automatically, so if you haven't already explored that avenue, try the free ones listed in our support article: Troubleshoot Firefox issues caused by malware.

And while you're at it... since this kind of annoying hijacker is usually part of a bundle, check for other unwanted programs that might have been installed:

Open the Windows Control Panel, Uninstall a Program. After the list loads, click the "Installed on" column heading to group the infections, I mean, additions, by date. This can help you associate undisclosed bundle items that snuck in with some software you agreed to install. Take out as much trash as possible here. (If in doubt, feel free to post a screenshot.)