Firefox with modified UA string: Google docs cannot load

[Sven Klages]

Dear All,

I am using a commercial server software (web frontend) which checks the UA string of my browser to assure that I am using "Google Chrome" browser when accessing the server.
When I use standard Firefox it fails to load (moaning about google chrome is required).

Here at work I am only allowed to use Firefox.

So I installed Firefox plugins like "User-Agent Switcher" to simply change my UA string to some Chrome string.
This works fine for my specific software (so I don't really know why they require Google Chrome for their software).

But as a side effect: Using Firefox and changing the UA strings makes Google Drive (Google Docs) unusable :-(
With a modified UA string I am not able to open any document from my Google Drive (tables, images, whatever), "Document cannot be loaded" (in German).
Funnily the document itself shows up for a few seconds and then it fails to load.

Any idea why this happens? Or how I can circumvent this issue (using FF)?

* Switching UA string back and forth is not an option, as I sometimes need Google Docs and the other frontend in parallel

* Using another browser is not an option neither

* Can I force Firefox to use a modified UA string for specific IPs or domains only?

System: Linux / Windows 7, Firefox ~50/51, non-admin

thanks,
Sven

[Barry Hunter]

Any idea why this happens?

I guess, the server sees the Chrome UA, sends some chrome specific data, which then somehow crashes Firefox. Docs is probably exploiting some Chrome only feature. 

Sending a Firefox UA, allows the server to send the Firefox compatible data-stream. 

 

Or how I can circumvent this issue (using FF)?

The only idea, I can think is find a 'hybrid' User-Agent, that Chrome 'enough' to fool this other application. But is not enough to fool Google Drive check. 

 

* Can I force Firefox to use a modified UA string for specific IPs or domains only?

That would mean finding a plugin with that feature :)

This one

https://addons.mozilla.org/en-us/firefox/addon/uacontrol/

 says "Control what gets sent as the User-Agent on a per-site basis."