Profiler main HTML interface is not accessible

The accessibility team has been working on performance issues in Firefox associated with accessibility use. Unfortunately we've found that the main interface isn't accessible to the visually impaired, which prevents members of the team from inspecting profiles.

We'd like to get this fixed, and the accessibility team may be able to help provide feedback on how this should be accomplished.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-674)