When a computer or hard drive crash, files can be corrupted.

First; Perform a System File Check to fix corrupted system files

Win 7, 8, 10, Vista: https://support.microsoft.com/en-us/kb/929833 Win XP: https://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/system_file_checker.mspx?mfr=true

Wiki - Windows 10 System File Check http://answers.microsoft.com/en-us/windows/wiki/windows_10-update/system-file-check-sfc-scan-and-repair-system-files/bc609315-da1f-4775-812c-695b60477a93

After the above; Let’s do a full clean re-install;

Download Firefox For All languages And Systems {web link}

Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86)

Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux

If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove the profiles folder.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ If there is a problem, start your Computer in safe mode and try again.

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia

FredMcD said

After the above; Let’s do a full clean re-install; Download Firefox For All languages And Systems {web link} Save the file. Then Close Firefox. Using your file browser, open the Programs Folder on your computer. Windows: C:\Program Files C:\Program Files (x86) Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one. Do Not remove the profiles folder. After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ If there is a problem, start your Computer in safe mode and try again. http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia

I was considering reinstalling. Before I do, will I lose my passwords and bookmarks?

Firefox comes in two or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.

.....

FredMcD said

Firefox comes in two or more folders on all computers. They are; Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user. If you remove the Firefox folder, the user profiles would not be affected.

If that's template response, I'm a little confused on the difference between the two folders. Is it okay to just change the folder name a bit?

Unless there is a problem with the profile, there is no need to change the names of these folders.

As to the Firefox program folder in the computers Programs Folder, it needs to be renamed or removed for a clean reinstall.

The reason for a clean install is in case of corrupt files.

FredMcD said

Unless there is a problem with the profile, there is no need to change the names of these folders. As to the Firefox program folder in the computers Programs Folder, it needs to be renamed or removed for a clean reinstall. The reason for a clean install is in case of corrupt files.

"In the computers Programs folder" I assume you mean the folder labeled "Mozilla Firefox" located in the folder "Program Files (x86)".

I changed it to "Mozilla Old Firefox". Is that okay? And is there anything else I need to do before uninstalling the old Firefox and installing the new one?

n_mcrae_1982 said

"In the computers Programs folder" I assume you mean the folder labeled "Mozilla Firefox" located in the folder "Program Files (x86)".

Yes

I changed it to "Mozilla Old Firefox". Is that okay? And is there anything else I need to do before uninstalling the old Firefox and installing the new one?

Go ahead with the installer.

FredMcD said

n_mcrae_1982 said

"In the computers Programs folder" I assume you mean the folder labeled "Mozilla Firefox" located in the folder "Program Files (x86)".

Yes

I changed it to "Mozilla Old Firefox". Is that okay? And is there anything else I need to do before uninstalling the old Firefox and installing the new one?

Go ahead with the installer.

Thank you! It worked!

Glad to help. Safe Surfing.