Two screenshots

I recently installed Spybot, and Immunized - would that affect FF?

Also using Avast Free and Win Firewall on Win 8.1

I can't reply to Comments in YouTube, either. A separate window pops up with nothing in it, then closes.

Can you try to start Firefox in Safe Mode to see if Firefox works properly with no error? You can start Firefox in Safe Mode below:

• Windows/Mac: Go to Help > Restart with add-ons disabled
• Linux: Run firefox -safe-mode in the Terminal/Konsole

If Firefox opens up fine with no problems, it's probably one of your extensions that's causing the issue. You can re-enable your add-ons one by one until you find the one that causes the issue upon being re-enabled.

I just tried it with no add-ons, and there was no change.

FF opens fine, it's specifically about working with YouTube.

It says what it's doing in the bottom left, but it's too fast to get all of it. When you want to Reply to a comment, a separate window pops up, and says it's doing something with Google Plus, then it closes.

You can try these steps in case of issues with web pages:

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• Hold down the Shift key and left-click the Reload button
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (Mac)

Clear the cache and cookies only from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"

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

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

Nothing, did not fix

When I click reply to comments in a YouTube, the separate window that pops up and then disappears says something about Google Plus in the bottom left corner.

Are you able to reply to comments in YouTube???

You need Google+ account to comment in YouTube.

Did you enabledSafeMode in YouTube. Disable and check it out

• https://support.google.com/youtube/answer/174084?hl=en

I went to the Google Plus Profile - so it's there - and then to YouTube - same thing.

Safety was OFF

Like I say, it works as expected in IE 11

If you are logged in to YouTube, and you go to Reply to a comment, are you able to do it? Does a small box pop up?

Does the same thing in FF 31.0

Create a new profile as a test to check if your current profile is causing the problems.
See Creating a profile:

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem
Profile Backup and Restore

• http://kb.mozillazine.org/Profile_backup
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Jay, before I try a new profile, would it be possible for you to please:

1.) verify for me that you are able to Reply to a comment on YouTube? Or,

2.) can you make a new Playlist on YouTube, as described above?

Reason: There are no other indications I would have a problem with my FF Profile. If I did, it seems like something else would not be working, like, I wouldn't see my Bookmarks toolbar

. . . also, what would cause my profile to become corrupted? Doing an update to FF (installing over the current version), as opposed de-installing, and then installing the stand-alone new version?

Still doesn't work in FF 31.0

Works in IE 11

Still doesn't work in FF 32.0.2

Works in IE 11

9/26/14 I see fixed in FF 32.0.3

Thank you :-)