Right-click Firefox spellcheck on Twitter deletes paragraphs when ScrollAnywhere is active

[MasterRahool]

Description:
When ScrollAnywhere is configured to use the right mouse button, it interferes with Firefox’s built-in spellcheck on Twitter’s text editor (contentEditable fields).

Steps to reproduce:

• Enable right-click activation in ScrollAnywhere.
• Go to Twitter, type multiple paragraphs into the compose box.
• Misspell a word in the second paragraph.
• Right-click the word and choose a correction from the context menu.

Result:
The word is corrected, but the second paragraph is replaced with a duplicate of the first paragraph, or is garbled with parts of the corrected text

Workaround:

If I hold Ctrl before right-clicking, the problem does not occur.
If I right-click first and then press Ctrl, the bug still occurs.

So right now my workaround is to use the 'disable with control held down' option, alternatively could whitelist x.com

So far I dont recall other sites doing this, but twitter/x has been consistent

Notes:
Seems like ScrollAnywhere is intercepting the right-click event in editable fields and causing Firefox’s spellcheck to apply to a broader selection than intended.

[Juraj-Masiar]

Thank you for the report!
I can reproduce it here.

The issue is a bit more complicated - you need to have the cursor in the different paragraph, then when you right click a word, you can see the cursor doesn't move. So the "spell check fix" is applied to the original position, not to the clicked word.

The fact that my addon can break default Firefox behavior this easily sounds like a bug in Firefox.
And if I'm seeing it right, in Chrome this doesn't happen.

I need to investigate this deeper though to see what my addon is actually doing.
Then I need to create a simple test case and then see if it happens in Firefox and not in Chrome and at that point, I'll report it to Firefox to see what they think.
Because currently I'm not sure I can fix it.
I'll try to allocate some time for this later this week.

[Juraj-Masiar]

So, I have some bad news AND some good news!

I've tried to create a simple case which I could report to Firefox team, but the issue doesn't reproduce anywhere else.
I've tried to use other "contenteditable" containers, and eventually I've copied the whole HTML page of twitter to see if it happens without their javascript:

But it works as expected.
This suggests that the issue is actually in the Twitter code (their javascript editor is doing some magic when it detects changes).

But I've checked my own code too and there is a special switch that allows not calling "preventDefault()" when mouse down happens.
And this seems to fix the issue!

Try to enable this and save changes and it should work now (as you right click, the cursor moves).

NOTE that the "preventDefault()" is there for a reason, so this may actually break the scrolling on some other pages, likely when page registers some "mosedown" handlers. This should be rare though...