Odd. I haven't noticed this happening (on Windows 7).

Are you saving the "complete" page with images and other related files, or "HTML only"?

Does it make any difference what the source of the .html file was, i.e., particular website?

If you right-click another kind of file Firefox can handle, such as a text file, and open it in Firefox, does it also open twice?

A standard diagnostic to bypass interference by extensions (and some custom settings) is to try Firefox's Safe Mode.

First, I recommend backing up your Firefox settings in case something goes wrong. See Back up and restore information in Firefox profiles. (You can copy your entire Firefox profile folder somewhere outside of the Mozilla folder.)

Next, restart Firefox in Firefox's Safe Mode (Diagnose Firefox issues using Troubleshoot Mode) using

Help > Restart with Add-ons Disabled

In the dialog, click "Start in Safe Mode."

If pages open without a duplicate, that would point to one of your extensions or custom settings as the problem.

Notice any difference?

I noticed the information on resetting Firefox.. I did this, and now the problem is gone.. I will try resetting (now that I know how) to solve problems in the future. Thanks at all.

Hi EngineeringGuy, if you used the Reset Firefox button, you should find an Old Firefox Settings folder on your desktop. I suggest keeping that around for a while in case you notice anything critical missing from your newly slimmed down Firefox settings folder.

If it happens again then you can first try some basic steps like these like posted above because an issue like this is likely caused by an extension:

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode

If it works in Safe mode or with all extensions (Tools > Add-ons > Extensions) disabled then try to find which is causing it by enabling one extension at a time until the problem reappears.

Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

You can also check for issues caused by DDE:

• http://kb.mozillazine.org/Windows_error_opening_Internet_shortcut_or_local_HTML_file_-_Firefox