Autocompletion not fully visible on Firefox

[barmac]

Describe the Bug

When I try to access autocomplete on Firefox, it is not usable because the tooltip is mostly hidden.

Steps to Reproduce

1. Use editor in Firefox
2. Trigger autocomplete
3. Now it happens

Expected Behavior

It should be fully visible.

Environment

• Host (Browser/Node version), if applicable: [e.g. MS Edge 18, Chrome 69, Node 10 LTS]
• OS: [e.g. Windows 7]
• Library version: [e.g. 2.0.0]

Context

Reported initially via slack

Related to https://github.com/camunda/web-modeler/issues/19197

[barmac]

Maybe useful:

• On firefox, codemirror uses position: absolute

• On chrome, it uses position: fixed

[barmac]

This may be a bug in codemirror (to check).

[barmac]

I cannot reproduce the problem in the codemirror demo, but it uses position: fixed as in Chrome