Separate Issue; Your System Details shows;

Installed Plug-ins

Shockwave Flash 26.0 r0 Shockwave Flash 21.0 r0
Having more than one version of a program may cause issues. You must remove the older programs. Then get the current full installer.

Flash: Grab the uninstaller from here:

http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html Uninstall Flash Player | Windows

http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-mac-os.html Uninstall Flash Player | Mac

Then reinstall the latest version.

Note: Windows users should download the active_x for Internet Explorer. and the plugin for Plugin-based browsers (like Firefox).

Note: Windows 8 and Windows 10 have built-in flash players and Adobe will cause a conflict. Install the plugin only. Not the active_x.

Flash Player Version 26.0.0.137

https://get.adobe.com/flashplayer/ Direct link scans current system and browser Note: Other software is offered in the download. <Windows Only>

https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Other software is offered in the download. <Windows Only>

See if there are updates for your graphics drivers https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration

The control keys (copy paste . . .) have not changed.

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

dickhitt said

I used to be able to use my CTRL key to cut, copy, and paste. Now, when I'm on the internet, the CTRL key takes me to another open tab.

Ctrl+x (cut), Ctrl+c (copy), and Ctrl+v (paste) should not trigger any of those.

Firefox will switch tabs if you use any of these:

• Ctrl+Tab => next tab (or cycles back to the first tab)
• Ctrl+Shift+Tab => previous tab (or cycles back to the last tab)
• Ctrl+1 => first tab ... Ctrl+8 => eighth tab
• Ctrl+9 => last tab

But having those mixed up with cut/copy/paste is hard to understand...

Does this occur on all sites, even in the simple forms on this site, or is it a problem only on one or a few sites? Any pattern to the circumstances where it happens?

As a footnote: if you paste a web address in the address bar and you already have a tab open to that address, the default action (displayed in the drop-down) may be "switch to tab." But I have no idea if that's where you're pasting.