I don't see it, either, but I only have about 5 minutes of experience with it.

Some mobile pages have a "full site" link, usually toward the bottom.

To submit requests for new features, you can use the Settings dialog:

• Tap the tabs button
• Tap the gear/wheel/cog icon
• Tap "Send Feedback" to open the feedback page

Actually, this might be a better place for feature suggestions as you notice things:

https://fxos-ios-browser.ideas.aha.io/ideas/new

See https://support.mozilla.org/en-US/kb/viewing-desktop-sites-firefox-ios