[Feature] Firefox extension

[myInstagramAlternative]

Hello gents,

Thanks for this awesome library.

I wanted to see if I could add support for Firefox extension, I used GPT-5.3-codex with instructions for every step. Because this falls under vibe coding I'm not going to be opening a PR (unless said so).

This PATCH adds support for Firefox extensions, fixes broken stop button (which was not working on Firefox), changes CSS around text area (which was not readable when dark mode is enabled on Firefox).
https://gist.github.com/myInstagramAlternative/13e6514c90d939eb4dc48e0b9df2a9d6

If you are willing to review PR I'll be happy to commit cleaner version and do more in-depth testing on Chrome before creating a PR. Thanks.

Community Communication / 社区沟通

• I will be polite and respectful. / 我会保持礼貌与尊重。
• I will share constructive, actionable suggestions. / 我会提供建设性、可行动的建议。
• I have read the CODE_OF_CONDUCT.md and CONTRIBUTING.md. / 我已阅读行为准则。