User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:66.0) Gecko/20100101 Firefox/66.0

Steps to reproduce:

prior to ff66 my custom search keywords were all prefixed with a hashtag character to prevent accidentally searching on them when it wasnt intended

Actual results:

after updating to firefox 66 my custom search keywords all stopped working. i tried various things including refreshing firefox but after that did nothing i tried removing the hashtag character from my search keywords as a final test and they suddenly started working again. i added the hash back how they were in ff56 and below and they stopped again.

Expected results:

i expected the search keywords to function properly as they did prior to ff66 and allow me to use a hash character in them

:mak I take it based on bug 1517140, comment 7 this should be duped to that bug?

pretty much yes, a leading char like # will be considered a restriction character, changing this in the old urlbar implementation, at this point, is complicate, because we'd need to add an async behavior (check if a token is a keyword) into a synchronous codebase. It's something we may re-evaluate once the Quantum Bar becomes the de-facto implementation for the urlbar.
But in general the current idea is that keywords with a leading restriction char should not be allowed, unfortunately we were never good at doing that kind of checks in the UI :(