Could you describe the steps needed to get to those tabs?

Regarding applications, if you mean this list --

orange Firefox button (or Tools menu) > Options > Applications

-- do you see the search box and a blank list area??

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 check if there is a compatibility update available.

If this hasn't helped then also try to delete the addons.sqlite file.

To get to Apps i go to the Tools menu>Apps and yes, i see a search box and a blank list area. P.S. Problem is allready solved.

Thank u for help!)