msvcrt.dll = Microsoft C Runtime Library

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

See if there are updates for your graphics drivers https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

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. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory.

Do Not remove the profiles folder.

Look for, and rename any Mozilla or Firefox program folders by adding .old to them. Do not rename the Mozilla Thunderbird folder if there is one.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. If all goes well, remove the OLD folders when you are done.

If there is a problem, start your Computer in safe mode and try again.

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Hi FredMcD -

Yes. Ran the SFC, clean. Video card is: nVIDIA GeForce 7300 GS - driver is the latest (but older!)

Older system, yes, but this happened directly after upgrade to FF 50.0 from previous FF version. Legacy system, but has important stuff on it.

Thanks. :)

Did you do a reinstall?

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. A small dialog should appear. Click Start In Safe Mode (not Refresh).

Is the problem still there?

No. Haven't performed a reinstall.

Need instructions on how to back up Favorites, Bookmarks, Themes, etc. Surprising is that all was working just fine, until FF 50.0, so I would like to see if anyone else has this problem.

Thanks.

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

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And one folder in the profile of each user on the computer.

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

These add-ons can be a great help by backing up and restoring Firefox

FEBE (Firefox Environment Backup Extension) {web link} FEBE allows you to quickly and easily backup your Firefox extensions, history, passwords, and more. In fact, it goes beyond just backing up -- It will actually rebuild your saved files individually into installable .xpi files. It will also make backups of files that you choose.

OPIE {web link} Import/Export extension preferences

Type about:support in the address bar and press enter.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

This is your current profile. Copy the folder As Is to a folder on a thumb drive, or wherever.

Here's what I did:

Completely uninstalled FF 50 from my system. Done according to official Mozilla procedure.

https://support.mozilla.org/en-US/kb/uninstall-firefox-from-your-computer#w_uninstall-firefox_3

Exported Bookmarks and Bookmarks Toolbar.

Then ran SFC - clean result. Used CCleaner for registry and cache - totally cleaned.

System is completely clean. Reinstalled FF 50. Imported Bookmarks and Bookmarks Toolbar.

Reinstalled Add-on's one by one.

As of this post, all is well - need a week. I will post back then. Earlier if said problem arises.

Thanks! :)

Keep us posted. Good luck.

Update.

This problem has not reoccurred since the clean install. I'm closing this ticket and thanks for the assistance!

"The procedure entry point strnlen could not be located in the dynamic link library msvcrt.dll" Same problem happen after todays update Using Firefox 50.0.2 don't want too uninstall RE-INSTALL i have so much website logins & passwords saved and book marks, i know i could backup bookmarks but finding all the add on's again and hoping nothing gets corrupted by uninstalling and re- insatlling plus Internet Explorer 8 don't work GOOD anymore SO HOW WOULD I download Firefox using Explorer 8 PLUS IT'S risky . must be another way fixing this I'm using windows xp pro 32 bit SP3 see picture for details of problem.

                                               Please help  Thanks :

Hi makingitbetter, I think it's interesting that your error message has this at the beginning of its title bar:

Close tab (Ctrl+w)

Were you in fact trying to close that tab when you got that error??

If you can still do a few other things in Firefox, please try this:

Clean Reinstall

We use this name, but it's not about removing your settings, it's about making sure the program files are clean (no inconsistent or alien code files). As described below, this process does not disturb your existing settings. You do not need to uninstall Firefox first.

It only takes a few minutes.

(A) Download a fresh installer for Firefox 50.0.2 from https://www.mozilla.org/firefox/all/ to a convenient location. (Scroll down to your preferred language.) Choose the "Windows" version (32-bit) rather than the 64-bit version for maximum plugin compatibility (and of course for 32-bit Windows systems).

(B) Exit out of Firefox (if applicable).

(C) Using Windows Explorer/My Computer, rename the program folder as follows:

32-bit Firefox on 64-bit Windows: Rename

C:\Program Files (x86)\Mozilla Firefox

to

C:\Program Files (x86)\OldFirefox

Other combinations: Rename

C:\Program Files\Mozilla Firefox

to

C:\Program Files\OldFirefox

(D) Run the installer you downloaded in step (A). It should automatically connect to your existing settings.*

Note: Some plugins may exist only in that OldFirefox folder. If something essential is missing, look in these folders:

• \OldFirefox\Plugins
• \OldFirefox\browser\plugins

* If in doubt, back up your profile: Back up and restore information in Firefox profiles.

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

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And one folder in the profile of each user on the computer.

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

beginning when loading webpage here another error see picture

makingitbetter said

beginning when loading webpage here another error see picture

Does that mean you cannot download the Firefox installer? If you need a direct path, let me know your Windows version and preferred language (e.g., U.S. English vs. another language).

Hi makingitbetter, have you tried starting Firefox in its Safe Mode? In Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

what i did ! disabled all add on's still have the problem made a backup of my profile folder RUN %APPDATA%\Mozilla\Firefox\Profiles\ copy paste to another drive just incase... I Download a fresh installer for Firefox 50.0.2 closed firefox rename Mozilla Firefox to oldfirefox

then run fresh installer Firefox 50.0.2 everything went good so far went to test it at aol.com

it Happen again The procedure entry point strnlen could not be located in the dynamic link library msvcrt.dll" no luck

Hi makingitbetter, it sounds as though the problem may be external. Did you already run the System File Checker mentioned earlier in this thread?

A post was flagged as Solved Problem. Please remove that flag. If you don’t, others that can help may not read this post.

Go to that message, and use the Undo link to its right.

I was searching the web and found; Important: Some malware camouflages itself as msvcrt.dll, particularly when located in the C:\Windows or C:\Windows\System32 folder.

You may have ad / mal-ware. Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.

okay i did Run TYPE "Sfc /scannow" good thing i had the original winxp pro Disk to make it work scan the system no errors found on windows

I guess there is a bug in the Firefox After last update 50.0.2 never had this problem before i use this computer everyday, You think it will be fix in the next updated ?

i did upload picture to show proof i did run 

"windows file protection scan" everything checked out okay.

https://social.technet.microsoft.com/Forums/windows/en-US/97a6b7fb-9c9b-48a5-85b4-bd10eb18b8e6/msvcrtdll-problem?forum=w7itproperf