Changes in debugger for VSCode

Since "Debugger for Firefox" VSCode plugin deprecate debugging of addons (strting from v1.8), UB@5.11 now represent itself as a regular browser page for remote debugger.

To use a VSCode debugger developer should either update a UB server to version 5.11 (and launch.json as described in UBJS WiKi) or downgrade a "Debugger for Firefox" VSCode plugin to version 1.7