bug(linux): problems typing in Firefox in Ubuntu 25.10

Split out from #14997:

@dyacob wrote:

> Trying again with Ubuntu 25.10 / keyman 18.0.244-1-sil1-questing / gff_amharic 3.3 it was different still:
>
> - GMail Compose the same behavior that [@merawi_mikre](https://community.software.sil.org/u/merawi_mikre) experienced, typing slower doesn’t seem to help. Apostrophe doesn’t work in the Firefox URL bar.
> - GEdit - Apostrophe does not work.
> - GNOME Terminal - better, the base letter replacement seems to work, but after type about 3 letters the behavior is like the backspace key is being held down, everything erases and the cursor keeps trying to go left but has hit the start of line.
There seems to be quite a few errors with Linux or at least with GTK-based apps. I am setup now to help testing any potential solutions.