Start Firefox in Safe Mode to check if one of the extension (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extension+and+themes

Create a new profile as a test to check if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

There are other things that need your attention.

Note that your System Details List shows multiple Flash plugins.

1. Shockwave Flash 13.0 r0
2. Shockwave Flash 12.0 r0

You can find the installation path of all plugins on the about:plugins page.

• http://kb.mozillazine.org/Issues_related_to_plugins#Identifying_installed_plugins

You can check the Flash player installation folder for multiple Flash player plugins and remove older version(s) of the plugin (NPSWF32) and possibly (re)install the latest Flash player.

• (32 bit Windows) C:\Windows\System32\Macromed\Flash\
• (64 bit Windows) C:\Windows\SysWOW64\Macromed\Flash\

I did these steps after first crash and nothing help.

Can you give me your crash reports?

1. Enter about:crashes in the Firefox address bar and press Enter. A Submitted Crash Reports list will appear, similar to the one shown below.
2. Copy the 5 most recent Report IDs that start with bp- and paste them into your response here.

New versions of Firefox could not work e.g. when you watch movie and play browser games ( like heroes-online.com) at same time for long period. Older versions stay stable. I don't have any of last reports from 29.0.1 because mozilla didn't collect data for bp after these crashes.

Have you tried disabling the Flash plugin's protected mode feature? This involves creating or editing a settings file. The following pages/posts provide different ways to do that:

• Adobe support article under the heading "Last Resort": Adobe Forums: How do I troubleshoot Flash Player's protected mode for Firefox?

• Manual steps: https://support.mozilla.org/questions/968190?page=5#answer-509209

• Batch file to automate the manual steps: https://support.mozilla.org/questions/982093#answer-518078

Flash needs to completely unload from memory (restarting Firefox might help) before this would take effect.

Any improvement?

I did it already in first time. I know that effects, but as I already said, older versions of mozilla allowed me to work for long periods without restarting browser or orther actions with it.