Fix clipboard copy in Firefox

[Candypopppsss]

What this PR does

Fixes the Copy Raw button silently failing in Firefox by adding a robust cross-browser clipboard implementation.

Root cause

navigator.clipboard.writeText can throw NotAllowedError in Firefox when the page doesn't have clipboard-write permission or the page isn't in active focus.

Fix

• Try navigator.clipboard.writeText first (Chrome, Edge, modern FF)
• Fall back to document.execCommand('copy') via a temporary textarea
• Show a sleek success or error toast message to the user after each attempt to provide clear visual feedback

Visual Previews

Success Toast	Error Toast

Testing

• Chrome ✅
• Firefox ✅ (was broken before)
• Edge ✅
• Safari ✅ (or N/A)
• No console errors

Closes #216

[Candypopppsss]

Hi! I have submitted a fix for the Firefox clipboard
bug. Would love a review when you get a chance
#216

[Karanjot786]

Hey @Candypopppsss! Saw your work on GSSoC 2026.

We are building TermUI, a TypeScript terminal UI framework with React-style hooks and JSX, rendered entirely in the terminal.

We have 99 unassigned GSSoC issues open across widgets, hooks, adapters, and CLI tooling. Your JavaScript background transfers directly.

• Open issues (GSSoC 2026)
• TermUI on GSSoC

Karanjot, TermUI maintainer

[Candypopppsss]

hi @Karanjot786 Thank you for your approach ! I'll look into it