try typing the add-ons names into the search box in the add-on manager (It is on the top right) and installing through that route, just to see if it works better. It is also the "preferred" installation method

Thanks for the reply. I did and it says it "could not find any matching add-ons."

I had closed and reopened Thunderbird and the Add-On mgr did not show Profile Switcher. I had closed it again and opened it and Profile Switcher was there. I clicked on the install and again as before it hangs and does not install.

It is possible that there is a problem with the file(s) that store the extensions registry.

Delete the extensions.* files (e.g. extensions.json, extensions.sqlite, extensions.ini) and compatibility.ini in the Firefox profile folder to reset the extensions registry.

• https://support.mozilla.org/kb/Profiles

New files will be created when required.

See "Corrupt extension files":

• http://kb.mozillazine.org/Unable_to_install_themes_or_extensions
• https://support.mozilla.org/kb/Unable+to+install+add-ons

If you see disabled or not compatible extensions in "Tools > Add-ons > Extensions" then click the Tools button at the left end of the Search Bar to check if there is a compatibility update available.

If this hasn't helped then also delete the addons.json and addons.sqlite files.

Thanks! I deleted the extensions in the extension folder as well as those mentioned above and it now installed ProfileSwitcher. Thanks again!!!