Only specific letters are recognized in Vimium's bar

Describe the bug

Either by opemning o/O or Shift+T, the Vimium bar opens. While Shift+T initially shows the last few entries, entering text in the bar doesn't really affect these results.

When entering anything, the list isn't being updated. Only some specific letters (like a, an, o and few others) do in fact work and upon entering them, the list updated. But that's quite a limited alphabet and renders these functions unuseable.

To Reproduce

Steps to reproduce the behavior:

1. Open your "last used tabs" list with Shift+T.
2. Enter the first letter a to filter results.
3. This shows any result with the letter a in it.
4. Continue filtering on adding the letters "assemble" for example.
5. The list stops filtering beneath the first letter a.

Browser and Vimium version

No source file, test, or entry point is named in the issue. First reproduce the Shift+T filtering problem in Firefox using the listed steps, then trace the bar's text-filtering behavior; done means successive letters such as “assemble” continue narrowing the results.