Sorry, I don't know what the "chambers" search engine is.

Search engines that come with Firefox can't be permanently removed by the user. If you delete one it will come back the next time Firefox is updated. Mozilla started "protecting" them back in Firefox 34.0.5 to prevent those search engines from being tampered with by malicious applications or by extensions. Plus there's also some type of "connection" with Mozilla agreements for placement of search engines in Firefox; seems to be 5 different search engines per locale build, with one being the Default per the locale. Users get the appropriate search engines for where they live, which differs by region / country / language. It also allows Firefox to remove a search engine when their agreement with a search engine ends; which Mozilla did somewhat recently with Yahoo! search, so I am surprised by you mentioning Yahoo. Maybe your Linux distro had / had their own agreement with Yahoo, which is permissible because many Linux distros build their own Firefox from source. At least those are my opinions as a long term Firefox user and my observations as to how Mozilla works.

Really all you need to do is to un-check a search that you don't use or don't like in the Preferences > Search under One-Click Search Engines; Firefox will respect your choice and just not use that search engine and it won't be re-enabled after an update.

This does look to be specific to the snap version on ubuntu. I used the default install of firefox (62.0) on ubuntu and it respects my decisions. I had recently switched to the snap version as firefox on ubuntu does not want to play nicely with password managers.