svg.disabled = 'true' hides the the UI icons in extensions
In "safest" security level
svg.disabled is set to
true in Tor Browser. This causes the UI icons in the latest versions of uBblock Origin and uMatrix to disappear.
The author of the extensions declined working on this with a note:
"I consider this a browser issue, to be reported to Firefox issue tracker. Extensions extend a browser abilities, they should not be subjected to restrictions which are meant to be imposed on web pages."
However as this is Tor Browser specific, I am reporting it here.