I fully accept this may be a user error. Possibly caused by a poorly implemented userscript or conflicting extension, or problematic site.

Sequence of actions:

1. Open the "Options page" for a script.
2. Time passes with the page open (this is highly variable making reproduction difficult)
3. Return to the "Options page" tab (never closed)

Problem:

I see a section of red-text on black background with the following lines:

can't access property "visit", l[he.qt] is undefined
Visited@options/index.js:1:56437
8387/<@common-ui.js:1:94149

can't access property "visit", l[he.qt] is undefined
Visited@options/index.js:1:56437
8387/<@common-ui.js:1:94149

Using FF's inspection feature:

<textarea id="unhandledError" readonly="" style="position: fixed !important; z-index: 1000000000 !important; left: 0px !important; right: 0px !important; bottom: 0px !important; background: rgb(0, 0, 0) !important; color: red !important; padding: 5px !important; font-size: 10px !important; line-height: 1 !important; box-sizing: border-box !important; height: 90px !important; border: medium !important; resize: none !important;" spellcheck="false"></textarea>

Expected result:

One of the following maybe:

• Preferably, no clutter
• A way to clear or dismiss the messages
• A setting somewhere

Devtools console contents:

Environment:

Userscript manager: Violentmonkey 2.34.0
injected into "page"
Platform: Firefox 147.0.3 linux x86-64

I am currently trying with a mostly no-op US on a couple of sites (LinkedIn and a local python -m http.server path port to see if it happens in a more controlled environment.