Try this -- it takes advantage of a partial (wildcard) attribute value match on the menu item to identify extensions:

/* Hide Extension Buttons on Context Menus */
menuitem[image*="moz-extension://"] .menu-iconic-left,
menu[image*="moz-extension://"] .menu-iconic-left {
  display: none;
}

https://developer.mozilla.org/docs/Web/CSS/Attribute_selectors

Yes that did the trick! Thank you for the prompt reply...

It's worth a mention that Firefox context menu items now have reduced padding-left with the exception of in-page search field context menus (menu items are still centered). When either your solution or my original approach are applied it leaves this particular menu with extension menu items where expected (left-sided) but the other items remain centered. If the padding-left value is set the same across all menus to defeat this, the #context-navigation element is thrown out of whack.

> with the exception of in-page search field context menus (menu items are still centered).

Hmm, I see that extra left padding on the context menu for this textarea. There's a checkmark for Check Spelling, so maybe that's why the space is there for certain menus. Firefox must have some way that it distinguishes between these menus, but... my time's up for poking at it.

Have you been using the Browser Toolbox for your exploration? There's a preference to force menus to stick open until you press Esc, which is necessary to use "click to inspect" with them.

• ui.popup.disable_autohide
• https://developer.mozilla.org/docs/Tools/Browser_Toolbox

Maybe this code that hides the icons works better as display:none move the label text to the left end.

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

#contentAreaContextMenu :is(menuitem[image*="moz-extension://"],menu[image*="moz-extension://"]) .menu-iconic-left { visibility: hidden !important; }

Yes I actively use the Browser Toolbox including the preference you refer to. I'll have another look at it and post back when I have a solution.

I posted some other code you can try a few seconds before your last post.

@cor-el Yes I had previously considered this and thank you, however, although it leaves the in-page search field context menu items centered, in the remaining #contentAreaContextMenu menus leave the extension items centered and not to the left as the icon is only 'hidden'.

My thoughts would be to address the in-page search field context menu itself. Will post back once I've had a look at it.

Not ideal but solves the issue...and thanks again to both of you for looking at this.

/* REMOVAL OF EXTENSION CONTEXT MENU ICONS */

menuitem[image*="moz-extension://"] .menu-iconic-left,
menu[image*="moz-extension://"] .menu-iconic-left {
 display: none !important;

}

/* SET PADDING-LEFT AS THE SAME VALUE ACROSS ALL RELEVANT MENUS INCLUDING TEXT-AREA CONTEXT MENUS */

menu, menuitem {
 padding-left: 13px !important;

}

/* FIX FOR CONTEXT NAVIGATION ITEMS */

#context-back, #context-forward, #context-reload, #context-bookmarkpage {
 padding-left: 0px !important;

}