Your Download Helper extension is many, many versions old. All issues with the downloading change in Firefox 36 were addressed months ago. Perhaps you disabled automatic updating in your Firefox? That affects your extensions, too.

To manually check for extension updates, you can use this method:

Open the Add-ons page using either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then on the right side, above the list, look for the "gear" button and choose Check for Updates. This may add a new "Updates available" item at the bottom of the left column, or it may annotate each of the extensions that has an available update, or both.

In some cases, you need to install the new Firefox first and THEN check for extension updates, because the update is not backwards compatible and won't show up for older versions of Firefox. This varies.

Firefox should retain your home page when you update. Avoid clicking any buttons that refer to speeding up Firefox by restoring default settings.

I noticed your Question Details > More System Details lists a user.js file.

Firefox uses the settings in that optional file at startup to override your saved preferences from the previous session. Unless you created that file yourself, it may contain settings from an add-on or external software. You can check and remove the file using the steps in this article: How to fix preferences that won't save.

Note: By default, Windows hides the .js extension on files. To work with files as accurately as possible, I suggest showing all file extensions. This Microsoft support article has the steps: http://windows.microsoft.com/en-us/wi.../show-hide-file-name-extensions.

If Firefox still cannot remember your preferred home page, could you describe when it switches, and anything else that seems helpful? For example:

• Every time you exit out of Firefox and start it up again
• Every time you shut down Windows and start it up again
• Other consistent interval (e.g., weekly)
• Randomly

Hmm, since the home page problem occurs on other systems for which we don't know the system details, could you indicate what page takes it place? That sometimes indicates a particular malware problem.

https://addons.mozilla.org/en-US/firefox/addon/video-downloadhelper/versions/

The DownloadHelper 4.9.24.1 you have was released September 5, 2014 by the author.

There have been several updates to this extension by the author since.

It is not the Firefox browser that supports the many Extensions out there in a Firefox version but the other way.