Thank you, John and Jason.  Great suggestions, I'll give these a try.

I don't have time to test in cloud, but most of the syntaxes are the same from on prem.

If you want it to do folder but open a single document if only one result result try adding the following to your querystring.

&openlfoneresult=true&newtab=disabled

Looks like a problem with the search syntax. The example in the documentation is

URL Parameter: 

https://ServerName/laserfiche/docview.aspx?db=dbName&id=EntryID&readonly=true

Search Syntax:

https://ServerName/laserfiche/browse.aspx?db=dbName#?search=SearchSyntax

Note that your example is missing the second ? before the search syntax piece and when adding a parameter it should follow the db name with an & which is the standard for listing multiple query string parameters in a URL.

You also seem to have a stray semicolon in there.

Your URL should probably be something more like

http://app.laserfiche.com/laserfiche/index.aspx?db=ClientRepo&view=search#?search={[Tax Certification]:[Parcel Number]="2907_00600500"}

I'm not sure where the view=search is coming from, so maybe it could be

http://app.laserfiche.com/laserfiche/index.aspx?db=ClientRepo#?view=search&search={[Tax Certification]:[Parcel Number]="2907_00600500"}

Basically you want the base URL to be 

http://app.laserfiche.com/laserfiche/index.aspx?db=ClientRepo

If you add a parameter to that, it should be with & like

http://app.laserfiche.com/laserfiche/index.aspx?db=ClientRepo&view=search

And the # is probably more of an indicator for breaking off the second set of query string parameters since more commonly there is only one set starting with ? and separated by &.

So you're appending #?search=[syntax] to that base URL.