Change Add-on Install Link based on Requesting Platform

[linuxwolf]

Fixes #124 Connected to #125

This changes the install button based on the user's current browser:

• Firefox 67 or higher --> "Install for Firefox" (link to add-on)

• Firefox before 67 --> "Upgrade Firefox" (link to Fx install)

  

• Not Firefox --> "Get Firefox" (link to Fx install)

  

[jaredhirsch]

@linuxwolf Also, it's probably fine, but there are some weird version strings like "67pre3" that you should double-check won't do strange things when parseInt'd: https://developer.mozilla.org/en-US/docs/Mozilla/Toolkit_version_format

[linuxwolf]

That, and moving to an external script actually broke the links.

Will have to think this through a bit more ...

[jaredhirsch]

ah yeah, I was wondering if the double-mustaches were going to get templated or not if they were added after initial page render. I would guess that we'd need to specify the complete link, or insert a client-side templating library to render those URLs dynamically

[linuxwolf]

ah yeah, I was wondering if the double-mustaches were going to get templated or not if they were added after initial page render. I would guess that we'd need to specify the complete link, or insert a client-side templating library to render those URLs dynamically

I was missing the frontmatter "secret sauce". Now links are correct (again).