Tor Browser vs Iridium Browser

If you follow their instructions religiously, Tor is the nec plus ultra in terms of safety and privacy. For the time being at least.

Can be installed and run on a portable device such as a USB stick.

Privacy. It's fundamental. And this browser has enabled and keeps enabling people to lookup things they don't want their ISP/ government or surveillance marketers to see.
And what's better they won't know a thing about what you searched.
What is visible to the outside world however is the fact: you make use of TOR and probably the TORBrowser this client / citizen of ours is using TOR to obfuscate his /her traffic (=~anonymize ).

Tor is just as safe as Chrome or firefox, as long as you don't visit malicious websites.

Firefox is a great browser, and tor is built on it

Open source builds trust on using the program

• Disable "Use a web service to help resolve navigation errors"
• Disable autocomplete through prediction service when typing in Omnibox
• Always send "Do-Not-Track" header
• Network/DNS prediction is disabled by default
• Block third-party cookies by default
• Link auditing (<a ping="...">) is disabled by default
• Fetch plugins list from iridiumbrowser.de where it will be updated regularly
• Site data (cookies, local storage, etc.) is only kept until exit, by default
• Passwords are not stored by default
• Input form autofill is disabled by default
• For IPv6 probes, use a DNS root server instead of Google
• The default search provider is Qwant
• Load "about:blank" on new tabs instead of the currently set search engine and/or promotions.
• Don't report Safe Browsing overrides.
• Don't use autofill download service.
• Disable cookies for safebrowsing background requests.
• Disable the battery status API.

Due to access to the Chrome Web store.

They won't update automatically in the background.

You are in control and you can do almost anything with the code.

Provides installers and packages for the most operating systems and linux distributions.

• Increase RSA keysize to 2048 bits for self-signed certificates (used by WebRTC)
• Generate a new WebRTC identity for each connection instead of reusing identities for 30 days
• Generate a new ECDHE keypair for each WebRTC connection instead of reusing them for multiple connections
• Disable using system-provided plugins (i.e. Java, Flash, etc.)

It is fast since all background services have been disabled or removed.

• Disable background mode
• Disable EV certificates, so they are shown just like "normal" certificates
• Disable Google cloud printing
• Disable Google hot word detection
• Disable Google experiments status check
• Disable Google translation service
• Disable Google promotion fetching
• Disable Google Cloud Messaging (GCM) status check
• Disable Google Now
• Disable automatic update check
• Disable profile-import on first run

Supports all the modern web features.