Prevent extension search engines from breaking the whole search system

We found that if an extension tries to add a search engine that is already bundled the whole search system breaks.

We should contain the damage (and then upstream the patch).

added Desktop Doing labels

assigned to @pierov

mentioned in merge request mullvad-browser!77 (merged)

added Uplift label

I've ran a try job before trying to uplift this, and found out it breaks unit tests.

So, I'm trying another version in which I revert the changes and re-throw the exception.

The new try build has passed all tests.

marked this issue as related to tor-browser-build#40914 (closed)

marked this issue as related to tor-browser-build#40915 (closed)

mentioned in issue #40789

added 13.0 stable label

added Bug label

Patch approved (but upstream didn't want the part to restore to the initial state).

Waiting for it to be landed then I'll open a MR to include it!

mentioned in merge request !769 (merged)

closed

removed Doing label

marked this issue as related to tor-browser-build#40965 (closed)

marked this issue as related to tor-browser-build#40966 (closed)