Thunderbird: Not possible to write a new message with ScrollAnywhere activated and LeftButton active

[sphh]

Describe the bug
I use ScrollAnywhere in Thunderbird on a tablet with touchscreen and pen input. It works well in the message pane, but not in the message list or folder panes. But what is more troubling, is that it becomes nearly impossible to write an email: You cannot place the cursor in the message input box.

Steps To Reproduce
Steps to reproduce the behavior:

1. Set ScrollAnywhere to use the Left button and tick all checkboxes under it.
2. Activate ScrollAnywhere.
3. Open a new Compose message window.
4. Try to position the cursor in this composer window:
   1. Clicking into the message input box does not show the cursor.
   2. Pressing TAB repeatedly does not position the cursor in the message input box.
   3. Only right-clicking into the message input box shows the cursor.
5. This has to be repeated everytime when you re-activate the composer window (e.g. you switch to another program and switch back to the composer window).

I tried with Single click and Double click and experience the same behaviour for both settings.

Expected behavior
The cursor should show in the message compose input box.

Device info:

• operating system: Linux Mint 20.1
• Browser and version: Thunderbird 78.7.1
• addon version: 8.7

[fastaddons]

Yeah, that left mouse scrolling is hard to do right.
Regarding the scrolling in the message list or folder panes - this is not possible, there is simply no API I could use to scroll those. If they add it in the future, I will for sure implement it because I miss it too.

Now the scrolling in the message is tricky, there seems to be multiple things that needs fixing:

1. When the message is opened, the focus is correctly on the first line but scrolling will steal the focus somehow somewhere... However even if I fix this, it would be still hard (or impossible) to position cursor back on top line once you click to the body below - since there is no text on the first line!

2. Single click to put cursor somewhere without text may be impossible. The mouse-down event on non-text is cancelled, otherwise you wouldn't be able to scroll. I could try to emit "fake click" event when I detect user only clicked and didn't scrolled. But I can't say if that will work. But if yes, that would be amazing fix!

3. Double click seems like an easy fix! I should be able to detect it in the second mouse-down event and not block it. But there is a good chance it will actually perform the "double-click" action, which is word selection. Still that may work on empty first line.

Not exactly piece of cake. I will look into it for the next version. But not now, I need to finish some urgent tasks for my speed dial addon.

[sphh]

Have you asked the TB developers about the API for the message list and folder panes? @jobisoft is always very responsive (I hope, he doesn't mind me mentioning him here, because he already has enough on his plate!)

Thanks for looking into the other item!

[fastaddons]

Nope, but that's actually a very good idea :).
I'll create feature request later today and post the link here.

[fastaddons]

Here the bugzilla request for the new API:
https://bugzilla.mozilla.org/show_bug.cgi?id=1701454
Let's see how it goes.