Try doing a Reset. You will need to reinstall your addons--make sure you take a screenshot (or write them down) so you know which you want to later reinstall.

https://support.mozilla.org/en-US/kb/reset-preferences-fix-problems

I did the Reset as you suggested. That seems to have solved the first two problems that I was pretty sure were a Firefox issue. However the problem still remains for these tow items. The Right Click problem is the most aggravating because I use it a lot.

If I happen to move my cursor over one of the icons on the taskbar, the little picture appears above the icon showing which screens were open which I like. However, now they don't disappear, even if I'm scrolling through a different application. I have to actually type something in a different application, or select the picture above the icon. They used to disappear when I moved the cursor off of the taskbar icon.

The other thing is that when I right click on the icon on the taskbar, for instance on Firefox, it would give me a menu to either open another Firefox window or close all the windows currently open. That menu no longer appears.

Are these Firefox issues or do you think they are Windows 10 related?

Also, Thunderbird crashes every time I close it, but I guess that should be directed to a different forum. And now it's saying my profile is missing or corrupt. It just never ends. It's late, so a battle for another day.

Hard to say if its a Windows 10 or Firefox issue. But I think it's safe to say that anything related to the taskbar on your desktop has to be a Win issue.

You said earlier that you are testing Firefox 43.0.4, have you tested 44.0?

Does it also happen to any other application you have running and has it's icon on the taskbar? Or is it just excluded to Firefox? (Aside from Thunderbird).

Another thing you can do is reset your settings for Windows 10. Make sure to choose the option to keep your files--you will lose your apps, so make sure to make a list and keep your registered keys somewhere safe outside your PC (printed on a piece of paper--etc). You want to only reset your personal settings that you've made to Windows. Here is a guide how to reset Win 10: http://www.laptopmag.com/articles/reset-windows-10-pc

But I caution you, don't do this until you get more tips from other Firefox experts. This can also be a bug between Mozilla and Win 10. Where having to reset your Win 10 would be completely unnecessary.

Please note I am using Win 7. I briefly tested Win 10 on this machine, and I didn't like a lot of things, plus it's usually a common issue with a new OS, that many bugs will need to be addressed. I plan on moving to Win 10 sometime after a year has gone by--hopefully by then they've put a fix to the most aggravating bugs.

Another thing, make sure you've got the up to date BIOS update to your Toshiba laptop.

Good luck.

Okay, you said something about testing 43.0.4. I really don't want to be testing any versions of Firefox. I've got waaaaaayyyy too many problems with Windows 10 to add a test version of Firefox into the mix.

I just downloaded this version since this was a new laptop. I really need a well tested version with few, if any, problems.

How can I go back to a previous version? That might solve all my problems. Could you give me the URL where I might find one?

Here's an addition to the reply above. I want to go back to the version that is compatible with the addon called NewTab Homepage.

You are not following me.

Please notice that you started with your first post by reporting that you were testing (using) Firefox 43.0.4. There was a new update to Firefox about a day ago. You should be using 44.0--since it's the latest Firefox version.

I won't reply anymore, because I fear I may be confusing you. Good luck. Hopefully someone else can suggest a fix.

If you have an issue with an addon- go to the addon developer's page to see if there is an update available--if not, They might need to update it.

Sorry, I think I'm confusing you. To me testing and using are vastly different based on past experience in Technologies.

I think Firefox either got updated automatically or accidentally on my part when I installed it on my new laptop. The last time it worked correctly for me was whatever version that was compatible with NewTab Homepage. I know this to be true because I use that option dozens of times a day. And now it no longer works.

I think possibly my problems started with whatever version of Firefox ceased being able to use that Add-in.

No, I am not have trouble with any Add-in. I was only using it as a point of reference for when Firefox seemed to work correctly for me.

Okay, I've finished solving this problem. The two items that were left unsolved, >>>>> If I happen to move my cursor over one of the icons on the taskbar, the little picture appears above the icon showing which screens were open which I like. However, now they don't disappear, even if I'm scrolling through a different application. I have to actually type something in a different application, or select the picture above the icon. They used to disappear when I moved the cursor off of the taskbar icon.

The other thing is that when I right click on the icon on the taskbar, for instance on Firefox, it would give me a menu to either open another Firefox window or close all the windows currently open. That menu no longer appears. >>>>>>> I managed to solve myself. I had run out of ideas with these two and I had also noticed that I was having a problem with MS Word if I copied something from the internet and pasted it in a Word document, it would take 20 or more minutes to paste the document. So just on a hunch, I went into the Control Panel/Programs and Features, and ran a Repair on Microsoft Office, rebooted the laptop, and now everything seems back to normal. This also solved a problem I was having with the Thunderbird email client. One of those Microsoft Mysteries, I guess. This can be considered solved.