Ensure extension works on Firefox about rolod0x

[0xAurelius]

Did some initial Firefox testing on Windows with v1.3.0 and noticed a few issues:

• Firefox defaults to extensions only being able to read and write data when the extension is clicked:
  
• Right click to save address doesn't seem to work, had to add it manually via the extension settings

[aspiers]

Have figured out a bunch of stuff and updated description above.

[aspiers]

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Build_a_cross_browser_extension may be useful.

[aspiers]

Thanks a lot! This matches my experience during (very limited) testing, and also my expectations. I think I know most of what's going on and hopefully won't be too hard to fix a lot of this.

[aspiers]

I get the impression from https://bugzilla.mozilla.org/show_bug.cgi?id=1766026 that Firefox intends to drop support for host_permissions, or already has done, in favour of optional_host_permissions. The former is the way rolod0x implements a list of built-in sites which are enabled by default. I guess we can start by having all sites disabled by default, and then if there's a way to automatically enable the most commonly used ones then we can add that later.

Right-click I'm pretty sure doesn't work due to the Firefox MV3 manifest not configuring the background worker in the right way.