FF: font size is not preserved when switching between editors

[Jakub Ś]

1. Go to replaceBycode sample
2. In the second editor, set the font size to 48, place the cursor at the end of the sample text and type few letters
3. Go to first editor place the cursor at the end of the sample text and type few letters (Do not change the font size)
4. Go to the second editor, place the cursor behind big letters and start typing
5. Letters are not 48 any more but have the default size.

[Garry Yao]

It's not related to instance focus switch, but the way how cursor is put into the editor, mouse click doesn't guarantee the same range position when return the focus, one of the following ways does:

1. Tab to re-focus the editor;
2. Click before the last character of the text line, press ARROW right once.

[Jakub Ś]

I believe this issue can be considered DUP of #8195