I have tried to add nosquint addon and am told will be added after restart, but nothing happens

The install dialog box says firefox in not allowing the, and I click the
allow button. I restart the computer, but nothing happens. I had no trouble install previously (I had a problem with a program and had to reinstall firefox. The addon does not come up on the toolbar.

Do you see that extension on the Tools > Add-ons > Extensions (about:addons) page?
It is possible that there is a problem with the file(s) that store the extensions registry.
Delete the files extensions.* (e.g. extensions.sqlite, extensions.ini, extensions.cache) 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, not compatible, extensions in "Tools > Add-ons > Extensions" then click the Tools button at the left side of the Search Bar (or click the "Find Updates" button in older Firefox versions) to do a compatibility check or see if there is a compatibility update available.

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