I doubt that a Mozilla/Firefox issue since ChatGPT4o isn't owned or operated by Mozilla/Firefox teams. And since there is no error reporting or error screenshot then falls onto ChatGPT4o to figure why their software doesn't work with Firefox.

Recent reports indicate that users of Firefox ESR (Extended Support Release) version 115.15 have encountered problems accessing ChatGPT and DALL-E. The issue stems from the absence of the Intl.Segmenter feature in this version, which ChatGPT relies on for text segmentation. Mozilla is aware of this compatibility issue, and future updates are expected to address it.

But you don't have version 115.15 ESR.

Firefox is up to date: Version 132.02 (64-bit). I would assume version 115.15 ESR is included. "Show Update History" doesn't allow going back that far. Not sure how to resolve.

Firefox 115 ESR is basically the old Firefox 115 Release but with allowed stability and security fixes since.

The older Firefox 115 ESR in only really being kept updated for the eol Windows 7, 8, 8.1 and macOS 10.12, 10.13, 10.14 OS users in mind since 115.16.0esr and later as Windows 10/11 and macOS 10.15+ users will be updated to current Release or 128 ESR.