Steps to reproduce:
- Set browser.urlbar.quantumbar true
- Set up a keyword search (for instance right click the search box on en.wikipedia.org and "Add a Keyword for this Search...")
- Type the keyword into the address bar
The last letter of the keyword gets highlighted in the dropdown, but it doesn't get inserted into the address bar, so when typing space next "wiki " becomes "wik " and the search therefore doesn't work.
This might depend on having a lot of stuff in the places db or cache, I haven't been able to reproduce it on a clean profile, and it doesn't happen with every keyword 100% of the time (in particular it seems to never happen with search keyword tied to a file: URL). mhowell has seen it as well, so it's not just my profile, though it might be Windows-specific. Toggling browser.urlbar.quantumbar makes it come and go.