Firefox: Right-clicking on multiple selected cells containing empty paragraphs removes the selection

[jswiderski]

Type of report

Bug

Provide detailed reproduction steps (if any)

1. Paste below table with paragraphs in Firefox into https://sdk.ckeditor.com/samples/table.html
   <table style="width:500px"><tbody><tr><td><p>&nbsp;</p></td><td><p>&nbsp;</p></td></tr><tr><td><p>&nbsp;</p></td><td><p>&nbsp;</p></td></tr></tbody></table>
2. Select all cells
3. Right-click on one of cells, select Cell Properties and apply Blue background.

Expected result

Selection stays and background gets applied to all cells.

Actual result

Selection disappears and background gets applied only to right-clicked cell.

Other details

Problem can only be reproduced in Firefox (both standard and ESR) but only when table contains empty paragraphs and right-click is performed on a cell with the empty paragraph.

If table doesn't contain empty paragraphs or right-click is performed on a cell with non-empty paragraph everything works as expected. Also by default the table inserted through toolbar button has no paragraphs so the problem doesn't occur there as well.

• Browser: Firefox
• OS: Windows
• CKEditor version: 4.9.2
• Installed CKEditor plugins: table, tableselection

[engineering-this]

After digging around:

Browsers I tested (including Firefox on MacOS) fire event contextmenu right after mousedown. However on Windows Firefox fires contextmenu after mouseup, and it changes selection between mousedown and mouseup. I'd propose to store selection when evt.data.$.button == 2 (which should refer to right click). And at this point add listener once( 'mouseup'... and restore selection.

Edit: I found piece of code from 2010 which produces this bug. PR is incoming.