[Affected versions]:
Firefox 66.0b13
Firefox 65.0

[Affected platforms]:
Windows 10 x64
macOS 10.14
Ubuntu 16.04 x64.

[Preconditions]:
Have some websites in "Manage Cookies and Site Data" settings, in about:preferences#privacy, "Cookies and Site Data" section "Manage Data" button.

[Steps to reproduce]:
1.Open Firefox
2.Go to about:preferences#privacy, "Cookies and Site Data" section
3.Click "Manage Data" button
4.Select more than one websites with shift+select or ctrl+select
5.Then click on "Site", "Cookies", "Storage" or anywhere on this window
6.Do this more then one time to reproduced the issue

[Expected result]:
The websites selected in step 4 should be deselected and the "Remove Selected" button should be grayed out

[Actual result]:
The websites selected in step 4 are still selected and "Remove Selected" button is still enabled.
Please see in attachment are two cases: - sometimes are some items selected and the "Remove Selected" button is grayed out

• sometime nothing is selected and "Remove Selected" button is enabled

[Regression range]:
This seems to be a regression, I will come back with regression range.

While checking for the regression range, I observe that, since the multiple selection functionality was introduced in Site Data Manager, this issue is present.

Last good: 2018.04.11 --> No multiple selection in site data manager.
First bad: 2018.04.12 --> Allow multiple selection in site data manager.

Potential regressor bug 1442183 - Allow multiple selection in the site data manager list. r=prathiksha

Here is a pushlog: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=0528a414c2a86dad0623779abde5301d37337934&tochange=da809ecceaf3a8ada0aa2d7115822d39d0439654

Bulk change of P3 carryover bugs to wontfix for 68.