Please explain the problem in detail. What happens? What is/are the exact error message(s) ?

don,t have my Customize button in menu

Customize Firefox controls, buttons and toolbars {web link}

Type about:customizing<enter> in the address bar.

Note: about:customizing is no longer present in Firefox 47+ releases.

• Press Alt or F10 to bring up the Menu Bar.Then View > Toolbars > Customize.
• Right-click on a blank spot in the toolbar and select Customize.

In the new window, look for the icon. When you find it, hold down the left button on it, and move it to where you want it to be. You can move any of the icons you want from here, but; some icons are locked in place.

There is also a Restore Defaults button at the bottom right.

. . . . plus running many processes in Firefox

More than one process is normal for the current Firefox. http://www.ghacks.net/2016/07/22/multi-process-firefox/

Multi-process Firefox is codenamed "e10s". https://wiki.mozilla.org/Firefox/multiprocess

You can right-click the "3-bar" Firefox menu button or empty space on a toolbar to find Customize. In the "3-bar" Firefox menu button drop-down list you can find it under "More Tools".

• https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars

Note that for some users Fission has been enabled as an experiment and if that is the case then there is additional site isolation and you will see more processes. You can check the current Fission state on the "Help -> More Troubleshooting Information" (about:support) page.

• https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox
• https://wiki.mozilla.org/Project_Fission
• https://hacks.mozilla.org/2021/05/introducing-firefox-new-site-isolation-security-architecture/