There are a few steps to try.
First, try resetting Firefox: https://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-most-problems
If this doesn’t solve the problem, trying using the Firefox Profile Manager to remove your old profile and create a new one manually:https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
If this still doesn’t work, try deleting the profile.ini file to force Firefox to create a new default profile:
Make sure that Firefox is closed
Press Windows key+R to open the Run box
Type: %APPDATA%\Mozilla\Firefox
Click “OK”
Delete the file called “profile.ini”
Run Firefox again
3. After pasting the above commands, please click File on the menu and click Save.
4. Type in NewFolder.reg as the file name, select to save the file on the Desktop. Click Save.
5. Go to the Desktop, and double click NewFolder.reg. A dialog box will pop-up saying "Are you sure you want to add the information in fix.reg to the registry?". Click Yes to confirm.
Go here: http://www.stardock.com/products/iconpackager/
and get the trial version of IconPackager, install it, use it to switch to any icon package, then switch back (if you want to) the standard windows icons.
And voila... all icons back.
Thanks!
Would you please try to choose the "Random Data 1 pass" , the recommended item, and do a erase again?
The recommended one is safe and fast, if the issue mentioned above still happens, please try to provide us a screenshot to further test this. Is that ok?
Please try the instruction below.
Step 1: Start the Windows Installer service.
a. Click Start, type Services.msc and press [ENTER]
b. Double-click Windows Installer.
c. Set the Startup type of Windows Installer to Manual.
d. Click Start to start the service. Note down the error message if any.
e. Click OK.
Step 2: Install the latest version of Windows Installer which you can download it from the link:
http://www.microsoft.com/downloads/details.aspx?FamilyID=5a58b56f-60b6-4412-95b9-54d056d6f9f4&displaylang=en
1. Click “start”and type “service”, you will get a picture like the picture below, see if the windows defender is listed.
2. If so, set its startup mode to automatically mode, then re-start the system.
3. If not, please download the file from the link below and run it. Restart the system and re-open the “service” according to step one and see if the startup type is automatically.
april's post in Fotmelding bij opstarten en open van Skype was marked as the answer