Sorry to hear about the crashes. Could you:

Create a new Firefox profile

A new profile will have your system-installed plugins (e.g., Flash) and extensions (e.g., security suite toolbars), but no themes, other extensions, or other customizations. It also should have completely fresh settings databases and a fresh cache folder.

This will be in parallel to your regular profile folder and if this new profile works, we can copy files from the old profile folder to recover some of your data like bookmarks and passwords.

Start up in the Profile Manager using Start > search box (or Run), type or paste the following and press Enter to run it:

firefox.exe -P

Don't delete anything here!

Any time you want to switch profiles, exit Firefox and return to this dialog.

Click the Create Profile button, assign a name like Sept2015, and skip the option to relocate the profile folder. After creating the profile, select it and start Firefox in that profile.

Is it stable?

(1) This article has a description of the files in your old profile folder and what they store: Recovering important data from an old profile. If you are going to copy files, I will give additional comments.

(2) When using the Profile Manager to switch between profiles, you might be tempted to use the Delete Profile button. But... it's a bit too easy to accidentally delete your "real" profile, so I recommend resisting the temptation. If you do want to clean up later, I suggest making a backup of all your profiles first in case something were to go wrong.

Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

You can check for problems with the sessionstore.js file in the Firefox profile folder that stores session data. Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost and you will have to recreate them (make a note or bookmark them if possible).

You can find the Firefox profile folder in this hidden location.

• %AppData%\Mozilla\Firefox\Profiles\<profile>\
• http://kb.mozillazine.org/Profile_folder_-_Firefox

"AppData" (XP: Application Data; Mac: ~/Library; Linux: ~/.mozilla) is a hidden folder.

• http://kb.mozillazine.org/Show_hidden_files_and_folders

Many thanks for jscher2000 and cor-el for their quick responses. I tried all (new profile, boot in secure mode) but crashes stay stable, no change.

I assume I have to get rid of all Firefox installation files and do a fresh install. I will loose passwords etc. but I have done a mozilla firefox backup some month ago.

Do you think this could solve the issue? Crome and IE are working fine.

Thank you. JanisMany thanks for jscher2000 and cor-el for their quick responses. I tried all (new profile, boot in secure mode) but crashes stay stable, no change.

I assume I have to get rid of all Firefox installation files and do a fresh install. I will loose passwords etc. but I have done a mozilla firefox backup some month ago.

Do you think this could solve the issue? Crome and IE are working fine.

Thank you. Janis

There are two main folders, the profile folder and the program folder. You can replace the program folder without much effort this way:

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, corrupted, or alien code files). As described below, this process does not disturb your existing settings. Do NOT uninstall Firefox, that's not needed.

(A) Download a fresh installer for Firefox 40.0.3 from https://www.mozilla.org/firefox/all/ to a convenient location. (Scroll down to your preferred language.)

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

(C) Rename the program folder, either:

(64-bit Windows folder names)

C:\Program Files (x86)\Mozilla Firefox

to

C:\Program Files (x86)\OldFirefox

(32-bit Windows folder names)

C:\Program Files\Mozilla Firefox

to

C:\Program Files\OldFirefox

(D) Run the installer you downloaded in (A). It should automatically connect to your last used profile.

Will a reinstalled Firefox start?

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

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

Thank for all the support. Also a new clean install didn´t bring the solution for me. I don´t know why?

I find in the WIndows event list, that a mozilla .dll report an error. Following this error on Google there was a statement that the cert8.db could be corrupted. I deleted this db and start Firefox. The problem was solved.

Thank you for all the hints.

Regards, Janis

+++++++++ skip this+++++++++++++

That was very good work. Well Done. Please flag your last post as Solved Problem so others will know.