Separate Issue; Your System Details shows;

Installed Plug-ins

Adobe PDF Plug-In For Firefox and Netscape 11.0.10 Adobe PDF Plug-In For Firefox and Netscape 11.0.0

Having more than one version of a program may cause issues.

Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites. Are there any problems?

Hi FredMcD, thanks for your help. I removed older Adobe plugin and modify settings regarding Hardware acceleration. Yes problem is present also on safe web sites.

You have a user.js file Please paste the contents of that in to your next reply (assuming it is not personal information).

The user.js file does not exist by default and unless you personally added it there is a possibility that malware did. The file is in your profile

• See Profiles - Where Firefox stores your bookmarks, passwords and other user data_how-do-i-find-my-profile
• Use Menu button {Three bar icon) -> Help {(?)icon) -> Troubleshooting information -> [Show folder]

I note you have VM Ware plugins, presumably that was all installed intentionally

In addition to trouble shooting by testing in Firefox's safemode could I also ask you to try Safe Mode plus

1. All Firefox plugins disabled
   • See Disable or remove Add-ons
2. Then also restarting in Windows Safemode (That is from the F8 key on most Windows versions)

What do you define as many tabs ? 10, 30, 100, hundreds

Look at Windows Task Manager (right click bar on bottom of screen for option) Is CPU or memory usage high and is page file in use ? Compare that with how it looks before it hangs.

_{(edit - typos Jan16th)}

Hi John99, thanks for your help.. Ok I removed user.js by my profile folder, in safe mode the problem seems to not be present but I'd like to try one day session with browser open. I confirm that vmware plugin was installed intentionally because I use that for my job. Computer resources are not under pressure during hang issue. Usually I open from 10 to 30 tab sessions but sometimes hang appear in new Firefox session with only 2-3 tabs opened. Kind regards

Good, you have made progress and can make the problem go away.

If the problem goes away in Firefox's safemode it could be Hardware Acceleration, but most likely will turn out to be one of your Firefox Extensions.

To troubleshoot further try in ordinary rather than safe mode, but with all extensions disabled. If that works ok enable half the extensions then bisect the selection sets until you find the problem.

Type about:addons<Enter> in the address bar to open your Add-ons Manager. Hot key; <Control>(Mac:<Command>)<Shift> A)

In the Add-ons Manager, on the left, select Extensions. Disable a few add-ons, then Restart Firefox.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All of them.

If the problem continues, disable some more (restarting FF). Continue until the problem is gone. After, you know what group is causing the issue. Re-enable the last group ONE AT A TIME (restarting FF) until the problem returns.

Once you think you found the problem, disable that and re-enable all the others, then restart again. Let us know who the suspect is detective.