You may be able to try this work around to customize the context menu http://dottech.org/157855/how-to-customize-firefox-right-click... however currently the menu will change based on where you right click in the browser.

In the past this has been fixed by disabling hardware acceleration as well please try this: You might need to restart Firefox in order for this to take effect, so save all work first (e.g., mail you are composing, online documents you're editing, etc.).

Then perform these steps:

1. Open Firefox Options window (Preferences on Mac or Linux) as follows:
   • In Firefox 29.0 and above, click the menu button and select Options for Windows or Preferences on Mac or Linux.
   • In Firefox 28.0 and previous versions, click the orange Firefox button at the top left, then select the "Options" button, or, if there is no Firefox button at the top, go to Tools > Options.
2. In the Firefox Options (or Preferences) window, click the Advanced tab, then select General.
3. In the settings list, you should find the Use hardware acceleration when available checkbox. Uncheck this checkbox.
4. Now, restart Firefox and see if the problems persist.

Additionally, please check for updates for your graphics driver by following the steps mentioned in the following Knowledge base articles:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

• Upgrade your graphics drivers to use hardware acceleration and WebGL

Did this fix your problems? Please report back to us!

Thank you.

The problem that menu's wouldn't shown (context-menu and also normal menus) have not been reproduced about 2 days.

I haven't try your solution because I had expected to try your solution after I encounter problem again.

Only difference when I had encounter menu problems is that I executed firefox from terminal prompt not from unity task bar .... (I expected to capture some relavant logs from terminal prompt when I encounterd menu problem again)

May be It takes some more hours or days before I encounter problem again or there are possiblity that I couldn't get that problem again until I do some alterations (restart firefox from unity ....)

My problem may be related to adobe flash I think ...

Menu-freezing occures after I used firefox specific times and whenever problem occures my adobe flash is outdated ...

So, I had experienced menu-freezing again and this time also adobe flash had had been outdated.

After I upgraded adobe flash plugin again, problem seems to be fixed.