[Affected versions]:

• Fx 65.0.2
• Fx 66.0b14
• Fx 67.0a1 (2019-03-11)

[Affected platforms]:

• Windows 7
• Windows 10

[Steps to reproduce]:

Precondition:
Download an en-US build, If from US be connected through a VPN to another country.

Method I

1. Install an antivirus (tested with Bitdefender and Web companion Lavasoft)
2. Install or unzip a Firefox build
3. Open a clean profile and go to about:preferences#search
4. Close the browser
5. Open another clean profile and go to about:preferences#search

Method II

1. Unzip a Firefox build
2. Open a clean profile and go to about:preferences#search
3. In about:config change the browser.search.region to US (eg. from RO) and trigger a restart
4. Close the browser
5. Open another clean profile and go to about:preferences#search

[Expected result]:

• No other search engine is displayed beside the default ones specific to their region.

[Actual result]:

• The eBay standard search engine is displayed as part of the default search engines.

[Regression range]:

• I will try to determine one asap.

[Additional Notes]:

Method I

• The same outcome occurs, regardless the order in which I install the Fx build/antivirus, or if I install the antivirus while the Fx browser is opened.
• Once I managed to triggered it only with the third profile, while two times, the eBay search engine was introduced with the first profile. But as a general behavior, second new created profile introduces this extra search engine.

Method II

• The eBay search engine is not directly inserted after the browser is restarted at step 3, and only when created a new profile.
• Note that at step 5, the newly created profile, although shows the extra eBay search engine (default for US region), the browser.search.region pref is set on the initial region (eg. RO).
• I couldn't reproduce the issue trough this method with an installed Firefox build.
• No antivirus is required to trigger this issue using this method.

This issue it doesn't look to be a regression. I can see it way back to Fx 43.0a1 (2015-08-18) using the steps from method II. Before this build, Ebay is displayed as default engine. But using the steps from method I, inconsistencies in displaying default engines are triggered even on older builds.

For en-US builds, there will always be an ebay, even if it is not available in that region.

We will switch it to the correct region if we have it (Australia for instance).

The actual list of default engines only changes when you install a different language version of Firefox.