This does not come with any version of Firefox install or as an update from Mozilla.

Perhaps this is being installed by one of your Extensions you have installed in Firefox or by a external software you have installed or updated recently.

https://support.mozilla.org/en-US/kb/what-search-hijacking https://support.mozilla.org/en-US/kb/remove-toolbar-has-taken-over-your-firefox-search https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware

Thanks for your reply James. If anyone has any specific information and steps to take to prevent this PUP being installed, I'd appreciate it.

All of the extensions I have are reasonably trustworthy and I would like to try to track down and block startpage from reinstalled.

I am aware of four ways to add a search engine to Firefox:

(1) An extension (2) Manually adding the search engine from the address bar of the search site (Autodiscovery) (3) Enterprise policy (https://mozilla.github.io/policy-templates/#searchengines--add) (4) The undocumented "browser.urlbar.update2.engineAliasRefresh" preference which adds a form to manually create a new search engine from the Settings page.

Since you trust your extensions not to be doing this, I'll skip #1 and mention how to investigate #3:

In the address bar, type or paste about:policies and press Enter to load the About Policies page. Normally, the "Active" panel just says "The Enterprise Policies service is inactive." Does yours list any active search policies?