fix: allow extension IDs to start with { for *Firefox*

[stevenxxiu]

Many Firefox extension IDs start with {, for example Violentmonkey has the extension ID {aecec67f-0d10-4fa7-b7c7-609a2db280cf}.

For example, I tested this works in the Installed scripts page, following https://github.com/gdh1995/vimium-c/wiki/Inject-into-other-extensions:

• In options/index.html, append <script type="application/javascript" src="/vimium_c_injector.js"></script>.
• Add the required vimium_c_injector.js to the root of the extension.